Add user avatar and profile feature, consolidate Auth and UserManagement features (#257)

web/backend/Features/Features.Users/Commands/Account/DeleteAccount/DeleteAccountCommand.cs

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+using MediatR;
+
+namespace Features.Auth.Commands.Account.DeleteAccount;
+
+/// <summary>Permanently deletes the given user account.</summary>
+/// <param name="UserAccountId">
+///     The authenticated caller's own ID, extracted from the access token -- never bind this from
+///     client-supplied input.
+/// </param>
+public record DeleteAccountCommand(Guid UserAccountId) : IRequest;

web/backend/Features/Features.Users/Commands/Account/DeleteAccount/DeleteAccountHandler.cs

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+using Domain.Exceptions;
+using Features.Auth.Identity;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Account.DeleteAccount;
+
+/// <summary>Handles <see cref="DeleteAccountCommand" /> by deleting the user via <see cref="UserManager{TUser}" />.</summary>
+public class DeleteAccountHandler(UserManager<ApplicationUser> userManager)
+    : IRequestHandler<DeleteAccountCommand>
+{
+    /// <exception cref="NotFoundException">Thrown when the account does not exist.</exception>
+    /// <exception cref="ConflictException">
+    ///     Thrown when the account cannot be deleted because other records (posts, comments, photos,
+    ///     follows) still reference it.
+    /// </exception>
+    public async Task Handle(DeleteAccountCommand request, CancellationToken cancellationToken)
+    {
+        ApplicationUser user =
+            await userManager.FindByIdAsync(request.UserAccountId.ToString())
+            ?? throw new NotFoundException("User account not found");
+
+        IdentityResult result = await userManager.DeleteAsync(user);
+        if (!result.Succeeded)
+        {
+            if (result.Errors.Any(e => e.Code == "AccountHasDependentRecords"))
+                throw new ConflictException(
+                    "Account cannot be deleted while it still has associated posts, comments, photos, or follows."
+                );
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+        }
+    }
+}

web/backend/Features/Features.Users/Commands/Account/UpdateEmail/UpdateEmailCommand.cs

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+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Account.UpdateEmail;
+
+/// <summary>
+///     Changes the email address of the given user account. The account's <c>EmailConfirmed</c> status
+///     is reset to unconfirmed as a result.
+/// </summary>
+/// <param name="UserAccountId">
+///     The authenticated caller's own ID, extracted from the access token -- never bind this from
+///     client-supplied input.
+/// </param>
+public record UpdateEmailCommand(Guid UserAccountId, string NewEmail)
+    : IRequest<UpdateEmailPayload>;

web/backend/Features/Features.Users/Commands/Account/UpdateEmail/UpdateEmailHandler.cs

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+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Account.UpdateEmail;
+
+/// <summary>
+///     Handles <see cref="UpdateEmailCommand" /> via <see cref="UserManager{TUser}" />.
+///     <see cref="UserManager{TUser}.SetEmailAsync" /> also resets <c>EmailConfirmed</c> to
+///     <see langword="false" />, so the user must re-confirm the new address (see
+///     <c>Features.Users.Commands.ResendConfirmationEmail</c>).
+/// </summary>
+public class UpdateEmailHandler(UserManager<ApplicationUser> userManager)
+    : IRequestHandler<UpdateEmailCommand, UpdateEmailPayload>
+{
+    /// <exception cref="NotFoundException">Thrown when the account does not exist.</exception>
+    /// <exception cref="ConflictException">Thrown when the requested email address is already in use.</exception>
+    public async Task<UpdateEmailPayload> Handle(
+        UpdateEmailCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user =
+            await userManager.FindByIdAsync(request.UserAccountId.ToString())
+            ?? throw new NotFoundException("User account not found");
+
+        IdentityResult result = await userManager.SetEmailAsync(user, request.NewEmail);
+        if (!result.Succeeded)
+        {
+            if (result.Errors.Any(e => e.Code == "DuplicateEmail"))
+                throw new ConflictException("Email address already exists");
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+        }
+
+        return new UpdateEmailPayload(user.Id, user.Email, user.EmailConfirmed);
+    }
+}

web/backend/Features/Features.Users/Commands/Account/UpdateEmail/UpdateEmailValidator.cs

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+using FluentValidation;
+
+namespace Features.Auth.Commands.Account.UpdateEmail;
+
+/// <summary>Validates <see cref="UpdateEmailCommand" />, mirroring the email rules in <c>RegisterUserValidator</c>.</summary>
+public class UpdateEmailValidator : AbstractValidator<UpdateEmailCommand>
+{
+    public UpdateEmailValidator()
+    {
+        RuleFor(x => x.NewEmail)
+            .NotEmpty()
+            .WithMessage("Email is required")
+            .EmailAddress()
+            .WithMessage("Invalid email format")
+            .MaximumLength(128)
+            .WithMessage("Email cannot exceed 128 characters");
+    }
+}

web/backend/Features/Features.Users/Commands/Account/UpdatePassword/UpdatePasswordCommand.cs

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+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Account.UpdatePassword;
+
+/// <summary>Changes the password of the given user account, verifying the current password first.</summary>
+/// <param name="UserAccountId">
+///     The authenticated caller's own ID, extracted from the access token -- never bind this from
+///     client-supplied input.
+/// </param>
+public record UpdatePasswordCommand(Guid UserAccountId, string CurrentPassword, string NewPassword)
+    : IRequest<UpdatePasswordPayload>;

web/backend/Features/Features.Users/Commands/Account/UpdatePassword/UpdatePasswordHandler.cs

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+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Account.UpdatePassword;
+
+/// <summary>
+///     Handles <see cref="UpdatePasswordCommand" /> via <see cref="UserManager{TUser}.ChangePasswordAsync" />,
+///     which verifies the current password before hashing and persisting the new one.
+/// </summary>
+public class UpdatePasswordHandler(UserManager<ApplicationUser> userManager)
+    : IRequestHandler<UpdatePasswordCommand, UpdatePasswordPayload>
+{
+    /// <exception cref="NotFoundException">Thrown when the account does not exist.</exception>
+    /// <exception cref="UnauthorizedException">Thrown when the current password does not match.</exception>
+    /// <exception cref="ConflictException">Thrown when the update otherwise fails.</exception>
+    public async Task<UpdatePasswordPayload> Handle(
+        UpdatePasswordCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user =
+            await userManager.FindByIdAsync(request.UserAccountId.ToString())
+            ?? throw new NotFoundException("User account not found");
+
+        IdentityResult result = await userManager.ChangePasswordAsync(
+            user,
+            request.CurrentPassword,
+            request.NewPassword
+        );
+        if (!result.Succeeded)
+        {
+            if (result.Errors.Any(e => e.Code == "PasswordMismatch"))
+                throw new UnauthorizedException("Current password is incorrect");
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+        }
+
+        return new UpdatePasswordPayload(user.Id, DateTime.UtcNow);
+    }
+}

web/backend/Features/Features.Users/Commands/Account/UpdatePassword/UpdatePasswordValidator.cs

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+using FluentValidation;
+
+namespace Features.Auth.Commands.Account.UpdatePassword;
+
+/// <summary>Validates <see cref="UpdatePasswordCommand" />, mirroring the password rules in <c>RegisterUserValidator</c>.</summary>
+public class UpdatePasswordValidator : AbstractValidator<UpdatePasswordCommand>
+{
+    public UpdatePasswordValidator()
+    {
+        RuleFor(x => x.CurrentPassword).NotEmpty().WithMessage("Current password is required");
+
+        RuleFor(x => x.NewPassword)
+            .NotEmpty()
+            .WithMessage("New password is required")
+            .MinimumLength(8)
+            .WithMessage("Password must be at least 8 characters")
+            .Matches("[A-Z]")
+            .WithMessage("Password must contain at least one uppercase letter")
+            .Matches("[a-z]")
+            .WithMessage("Password must contain at least one lowercase letter")
+            .Matches("[0-9]")
+            .WithMessage("Password must contain at least one number")
+            .Matches("[^a-zA-Z0-9]")
+            .WithMessage("Password must contain at least one special character")
+            .NotEqual(x => x.CurrentPassword)
+            .WithMessage("New password must be different from the current password");
+    }
+}

web/backend/Features/Features.Users/Commands/Account/UpdateUsername/UpdateUsernameCommand.cs

@@ -0,0 +1,12 @@
+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Account.UpdateUsername;
+
+/// <summary>Changes the username of the given user account.</summary>
+/// <param name="UserAccountId">
+///     The authenticated caller's own ID, extracted from the access token -- never bind this from
+///     client-supplied input.
+/// </param>
+public record UpdateUsernameCommand(Guid UserAccountId, string NewUsername)
+    : IRequest<UpdateUsernamePayload>;

web/backend/Features/Features.Users/Commands/Account/UpdateUsername/UpdateUsernameHandler.cs

@@ -0,0 +1,36 @@
+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Account.UpdateUsername;
+
+/// <summary>Handles <see cref="UpdateUsernameCommand" /> via <see cref="UserManager{TUser}" />.</summary>
+public class UpdateUsernameHandler(UserManager<ApplicationUser> userManager)
+    : IRequestHandler<UpdateUsernameCommand, UpdateUsernamePayload>
+{
+    /// <exception cref="NotFoundException">Thrown when the account does not exist.</exception>
+    /// <exception cref="ConflictException">Thrown when the requested username is already taken.</exception>
+    public async Task<UpdateUsernamePayload> Handle(
+        UpdateUsernameCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user =
+            await userManager.FindByIdAsync(request.UserAccountId.ToString())
+            ?? throw new NotFoundException("User account not found");
+
+        IdentityResult result = await userManager.SetUserNameAsync(user, request.NewUsername);
+        if (!result.Succeeded)
+        {
+            if (result.Errors.Any(e => e.Code == "DuplicateUserName"))
+                throw new ConflictException("Username already exists");
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+        }
+
+        return new UpdateUsernamePayload(user.Id, user.UserName);
+    }
+}

web/backend/Features/Features.Users/Commands/Account/UpdateUsername/UpdateUsernameValidator.cs

@@ -0,0 +1,20 @@
+using FluentValidation;
+
+namespace Features.Auth.Commands.Account.UpdateUsername;
+
+/// <summary>Validates <see cref="UpdateUsernameCommand" />, mirroring the username rules in <c>RegisterUserValidator</c>.</summary>
+public class UpdateUsernameValidator : AbstractValidator<UpdateUsernameCommand>
+{
+    public UpdateUsernameValidator()
+    {
+        RuleFor(x => x.NewUsername)
+            .NotEmpty()
+            .WithMessage("Username is required")
+            .Length(3, 64)
+            .WithMessage("Username must be between 3 and 64 characters")
+            .Matches("^[a-zA-Z0-9._-]+$")
+            .WithMessage(
+                "Username can only contain letters, numbers, dots, underscores, and hyphens"
+            );
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/ConfirmUser/ConfirmUserCommand.cs

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+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Authentication.ConfirmUser;
+
+/// <summary>Validates a confirmation token and confirms the corresponding user account.</summary>
+public record ConfirmUserCommand(string Token) : IRequest<ConfirmationPayload>;

web/backend/Features/Features.Users/Commands/Authentication/ConfirmUser/ConfirmUserHandler.cs

@@ -0,0 +1,41 @@
+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using Features.Auth.Services;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Authentication.ConfirmUser;
+
+/// <summary>
+///     Handles <see cref="ConfirmUserCommand" /> by validating the confirmation token and marking the
+///     corresponding user account as confirmed.
+/// </summary>
+public class ConfirmUserHandler(
+    UserManager<ApplicationUser> userManager,
+    IUserEmailStore<ApplicationUser> emailStore,
+    ITokenService tokenService
+) : IRequestHandler<ConfirmUserCommand, ConfirmationPayload>
+{
+    /// <exception cref="UnauthorizedException">
+    ///     Thrown when the confirmation token is invalid or expired, or when the associated user account cannot be found.
+    /// </exception>
+    public async Task<ConfirmationPayload> Handle(
+        ConfirmUserCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ValidatedToken validatedToken = await tokenService.ValidateConfirmationTokenAsync(
+            request.Token
+        );
+
+        ApplicationUser? user = await userManager.FindByIdAsync(validatedToken.UserId.ToString());
+        if (user == null)
+            throw new UnauthorizedException("User account not found");
+
+        await emailStore.SetEmailConfirmedAsync(user, true, cancellationToken);
+        await userManager.UpdateAsync(user);
+
+        return new ConfirmationPayload(user.Id, DateTime.UtcNow);
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/Login/LoginCommand.cs

@@ -0,0 +1,10 @@
+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Authentication.Login;
+
+/// <summary>
+///     Authenticates a user using their username and password and issues new tokens. Bound directly
+///     from the request body of <c>POST /api/auth/login</c>.
+/// </summary>
+public record LoginCommand(string Username, string Password) : IRequest<LoginPayload>;

web/backend/Features/Features.Users/Commands/Authentication/Login/LoginHandler.cs

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+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using Features.Auth.Services;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Authentication.Login;
+
+/// <summary>
+///     Handles <see cref="LoginCommand" /> by verifying credentials via
+///     <see cref="UserManager{TUser}" /> and issuing access/refresh tokens.
+/// </summary>
+public class LoginHandler(UserManager<ApplicationUser> userManager, ITokenService tokenService)
+    : IRequestHandler<LoginCommand, LoginPayload>
+{
+    /// <exception cref="UnauthorizedException">
+    ///     Thrown when the username does not match any account or the supplied password does not match
+    ///     the stored hash.
+    /// </exception>
+    public async Task<LoginPayload> Handle(
+        LoginCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user =
+            await userManager.FindByNameAsync(request.Username)
+            ?? throw new UnauthorizedException("Invalid username or password.");
+
+        if (!await userManager.CheckPasswordAsync(user, request.Password))
+            throw new UnauthorizedException("Invalid username or password.");
+
+        string accessToken = tokenService.GenerateAccessToken(user.Id, user.UserName);
+        string refreshToken = tokenService.GenerateRefreshToken(user.Id, user.UserName);
+
+        return new LoginPayload(user.Id, user.UserName, refreshToken, accessToken);
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/Login/LoginValidator.cs

@@ -0,0 +1,14 @@
+using FluentValidation;
+
+namespace Features.Auth.Commands.Authentication.Login;
+
+/// <summary>Validates that <see cref="LoginCommand.Username" /> and <see cref="LoginCommand.Password" /> are present.</summary>
+public class LoginValidator : AbstractValidator<LoginCommand>
+{
+    public LoginValidator()
+    {
+        RuleFor(x => x.Username).NotEmpty().WithMessage("Username is required");
+
+        RuleFor(x => x.Password).NotEmpty().WithMessage("Password is required");
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/RefreshToken/RefreshTokenCommand.cs

@@ -0,0 +1,10 @@
+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Authentication.RefreshToken;
+
+/// <summary>
+///     Exchanges a valid refresh token for a new access/refresh token pair. Constructed from the
+///     <c>X-Refresh-Token</c> header of <c>POST /api/auth/refresh</c>.
+/// </summary>
+public record RefreshTokenCommand(string RefreshToken) : IRequest<LoginPayload>;

web/backend/Features/Features.Users/Commands/Authentication/RefreshToken/RefreshTokenHandler.cs

@@ -0,0 +1,31 @@
+using Features.Auth.Dtos;
+using Features.Auth.Services;
+using MediatR;
+
+namespace Features.Auth.Commands.Authentication.RefreshToken;
+
+/// <summary>
+///     Handles <see cref="RefreshTokenCommand" /> by validating the refresh token and issuing a new
+///     access/refresh token pair.
+/// </summary>
+public class RefreshTokenHandler(ITokenService tokenService)
+    : IRequestHandler<RefreshTokenCommand, LoginPayload>
+{
+    /// <exception cref="Domain.Exceptions.UnauthorizedException">
+    ///     Thrown when the refresh token is invalid or expired, or when the user account it refers to no
+    ///     longer exists.
+    /// </exception>
+    public async Task<LoginPayload> Handle(
+        RefreshTokenCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        RefreshTokenResult result = await tokenService.RefreshTokenAsync(request.RefreshToken);
+        return new LoginPayload(
+            result.UserId,
+            result.Username,
+            result.RefreshToken,
+            result.AccessToken
+        );
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/RefreshToken/RefreshTokenValidator.cs

@@ -0,0 +1,12 @@
+using FluentValidation;
+
+namespace Features.Auth.Commands.Authentication.RefreshToken;
+
+/// <summary>Validates that <see cref="RefreshTokenCommand.RefreshToken" /> is present.</summary>
+public class RefreshTokenValidator : AbstractValidator<RefreshTokenCommand>
+{
+    public RefreshTokenValidator()
+    {
+        RuleFor(x => x.RefreshToken).NotEmpty().WithMessage("Refresh token is required");
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/RegisterUser/RegisterUserCommand.cs

@@ -0,0 +1,28 @@
+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Authentication.RegisterUser;
+
+/// <summary>
+///     Registers a new user account. Bound directly from the request body of <c>POST /api/auth/register</c>.
+/// </summary>
+/// <param name="Username">
+///     The desired username; must be 3-64 characters and contain only letters, numbers, dots,
+///     underscores, and hyphens.
+/// </param>
+/// <param name="FirstName">The user's first name; up to 128 characters.</param>
+/// <param name="LastName">The user's last name; up to 128 characters.</param>
+/// <param name="Email">The user's email address; up to 128 characters and must be a valid email format.</param>
+/// <param name="DateOfBirth">The user's date of birth; the user must be at least 19 years old.</param>
+/// <param name="Password">
+///     The desired plaintext password; must be at least 8 characters and contain an uppercase letter, a
+///     lowercase letter, a number, and a special character.
+/// </param>
+public record RegisterUserCommand(
+    string Username,
+    string FirstName,
+    string LastName,
+    string Email,
+    DateTime DateOfBirth,
+    string Password
+) : IRequest<RegistrationPayload>;

web/backend/Features/Features.Users/Commands/Authentication/RegisterUser/RegisterUserHandler.cs

@@ -0,0 +1,90 @@
+using Domain.Entities;
+using Domain.Exceptions;
+using Features.Auth.Commands.Profile.CreateUserProfile;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using Features.Auth.Services;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+using Shared.Application.Emails;
+
+namespace Features.Auth.Commands.Authentication.RegisterUser;
+
+/// <summary>
+///     Handles <see cref="RegisterUserCommand" />: creates the user via <see cref="UserManager{TUser}" />
+///     (which validates uniqueness and hashes the password), issues access/refresh/confirmation tokens, and
+///     attempts to send the registration confirmation email via Features.Emails.
+/// </summary>
+public class RegisterUserHandler(
+    UserManager<ApplicationUser> userManager,
+    ITokenService tokenService,
+    IMediator mediator
+) : IRequestHandler<RegisterUserCommand, RegistrationPayload>
+{
+    /// <exception cref="ConflictException">
+    ///     Thrown when an existing account already has the same username or email address, or when user
+    ///     creation otherwise fails.
+    /// </exception>
+    public async Task<RegistrationPayload> Handle(
+        RegisterUserCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user = new UserAccount
+        {
+            Username = request.Username,
+            Email = request.Email,
+            FirstName = request.FirstName,
+            LastName = request.LastName,
+            DateOfBirth = request.DateOfBirth,
+        }.ToApplicationUser();
+
+        IdentityResult result = await userManager.CreateAsync(user, request.Password);
+        if (!result.Succeeded)
+        {
+            if (result.Errors.Any(e => e.Code is "DuplicateUserName" or "DuplicateEmail"))
+                throw new ConflictException("Username or email already exists");
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+        }
+
+        await mediator.Send(new CreateUserProfileCommand(user.Id, string.Empty), cancellationToken);
+
+        string accessToken = tokenService.GenerateAccessToken(user.Id, user.UserName);
+        string refreshToken = tokenService.GenerateRefreshToken(user.Id, user.UserName);
+        string confirmationToken = tokenService.GenerateConfirmationToken(user.Id, user.UserName);
+
+        if (string.IsNullOrEmpty(accessToken) || string.IsNullOrEmpty(refreshToken))
+            return new RegistrationPayload(
+                user.Id,
+                user.UserName,
+                string.Empty,
+                string.Empty,
+                false
+            );
+
+        bool emailSent = false;
+        try
+        {
+            await mediator.Send(
+                new SendRegistrationEmailCommand(user.FirstName, user.Email, confirmationToken),
+                cancellationToken
+            );
+            emailSent = true;
+        }
+        catch (Exception ex)
+        {
+            await Console.Error.WriteLineAsync(ex.Message);
+            Console.WriteLine("Could not send email.");
+        }
+
+        return new RegistrationPayload(
+            user.Id,
+            user.UserName,
+            refreshToken,
+            accessToken,
+            emailSent
+        );
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/RegisterUser/RegisterUserValidator.cs

@@ -0,0 +1,63 @@
+using FluentValidation;
+
+namespace Features.Auth.Commands.Authentication.RegisterUser;
+
+/// <summary>
+///     Validates the field-level constraints on <see cref="RegisterUserCommand" />: username format and
+///     length, name lengths, email format, minimum age of 19, and password complexity.
+/// </summary>
+public class RegisterUserValidator : AbstractValidator<RegisterUserCommand>
+{
+    public RegisterUserValidator()
+    {
+        RuleFor(x => x.Username)
+            .NotEmpty()
+            .WithMessage("Username is required")
+            .Length(3, 64)
+            .WithMessage("Username must be between 3 and 64 characters")
+            .Matches("^[a-zA-Z0-9._-]+$")
+            .WithMessage(
+                "Username can only contain letters, numbers, dots, underscores, and hyphens"
+            );
+
+        RuleFor(x => x.FirstName)
+            .NotEmpty()
+            .WithMessage("First name is required")
+            .MaximumLength(128)
+            .WithMessage("First name cannot exceed 128 characters");
+
+        RuleFor(x => x.LastName)
+            .NotEmpty()
+            .WithMessage("Last name is required")
+            .MaximumLength(128)
+            .WithMessage("Last name cannot exceed 128 characters");
+
+        RuleFor(x => x.Email)
+            .NotEmpty()
+            .WithMessage("Email is required")
+            .EmailAddress()
+            .WithMessage("Invalid email format")
+            .MaximumLength(128)
+            .WithMessage("Email cannot exceed 128 characters");
+
+        RuleFor(x => x.DateOfBirth)
+            .NotEmpty()
+            .WithMessage("Date of birth is required")
+            .LessThan(DateTime.Today.AddYears(-19))
+            .WithMessage("You must be at least 19 years old to register");
+
+        RuleFor(x => x.Password)
+            .NotEmpty()
+            .WithMessage("Password is required")
+            .MinimumLength(8)
+            .WithMessage("Password must be at least 8 characters")
+            .Matches("[A-Z]")
+            .WithMessage("Password must contain at least one uppercase letter")
+            .Matches("[a-z]")
+            .WithMessage("Password must contain at least one lowercase letter")
+            .Matches("[0-9]")
+            .WithMessage("Password must contain at least one number")
+            .Matches("[^a-zA-Z0-9]")
+            .WithMessage("Password must contain at least one special character");
+    }
+}

web/backend/Features/Features.Users/Commands/Authentication/ResendConfirmationEmail/ResendConfirmationEmailCommand.cs

@@ -0,0 +1,6 @@
+using MediatR;
+
+namespace Features.Auth.Commands.Authentication.ResendConfirmationEmail;
+
+/// <summary>Resends the account confirmation email to a user, generating a fresh confirmation token.</summary>
+public record ResendConfirmationEmailCommand(Guid UserId) : IRequest;

web/backend/Features/Features.Users/Commands/Authentication/ResendConfirmationEmail/ResendConfirmationEmailHandler.cs

@@ -0,0 +1,41 @@
+using Features.Auth.Identity;
+using Features.Auth.Services;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+using Shared.Application.Emails;
+
+namespace Features.Auth.Commands.Authentication.ResendConfirmationEmail;
+
+/// <summary>
+///     Handles <see cref="ResendConfirmationEmailCommand" /> by generating a fresh confirmation token and
+///     sending it via Features.Emails.
+/// </summary>
+/// <remarks>
+///     Returns silently without sending an email if the user does not exist (to prevent user enumeration)
+///     or if the user's account is already verified.
+/// </remarks>
+public class ResendConfirmationEmailHandler(
+    UserManager<ApplicationUser> userManager,
+    ITokenService tokenService,
+    IMediator mediator
+) : IRequestHandler<ResendConfirmationEmailCommand>
+{
+    public async Task Handle(
+        ResendConfirmationEmailCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser? user = await userManager.FindByIdAsync(request.UserId.ToString());
+        if (user == null)
+            return; // Silent return to prevent user enumeration
+
+        if (await userManager.IsEmailConfirmedAsync(user))
+            return; // Already confirmed, no-op
+
+        string confirmationToken = tokenService.GenerateConfirmationToken(user.Id, user.UserName);
+        await mediator.Send(
+            new SendResendConfirmationEmailCommand(user.FirstName, user.Email, confirmationToken),
+            cancellationToken
+        );
+    }
+}

web/backend/Features/Features.Users/Commands/Profile/CreateUserProfile/CreateUserProfileCommand.cs

@@ -0,0 +1,6 @@
+using MediatR;
+
+namespace Features.Auth.Commands.Profile.CreateUserProfile;
+
+/// <summary>Creates a new user profile for a user account.</summary>
+public record CreateUserProfileCommand(Guid UserAccountId, string Biography) : IRequest<Guid>;

web/backend/Features/Features.Users/Commands/Profile/CreateUserProfile/CreateUserProfileHandler.cs

@@ -0,0 +1,19 @@
+using Features.Auth.Repository;
+using MediatR;
+
+namespace Features.Auth.Commands.Profile.CreateUserProfile;
+
+/// <summary>Handles <see cref="CreateUserProfileCommand" /> by inserting the new profile record.</summary>
+public class CreateUserProfileHandler(IUserProfileRepository userProfileRepository)
+    : IRequestHandler<CreateUserProfileCommand, Guid>
+{
+    public Task<Guid> Handle(
+        CreateUserProfileCommand request,
+        CancellationToken cancellationToken
+    ) =>
+        userProfileRepository.CreateProfileAsync(
+            request.UserAccountId,
+            request.Biography,
+            cancellationToken
+        );
+}

web/backend/Features/Features.Users/Commands/Profile/UpdateBiography/UpdateBiographyCommand.cs

@@ -0,0 +1,10 @@
+using MediatR;
+
+namespace Features.Auth.Commands.Profile.UpdateBiography;
+
+/// <summary>Updates the biography of the given user account's profile.</summary>
+/// <param name="UserAccountId">
+///     The authenticated caller's own ID, extracted from the access token -- never bind this from
+///     client-supplied input.
+/// </param>
+public record UpdateBiographyCommand(Guid UserAccountId, string Biography) : IRequest;

web/backend/Features/Features.Users/Commands/Profile/UpdateBiography/UpdateBiographyHandler.cs

@@ -0,0 +1,19 @@
+using Features.Auth.Repository;
+using MediatR;
+
+namespace Features.Auth.Commands.Profile.UpdateBiography;
+
+/// <summary>Handles <see cref="UpdateBiographyCommand" /> by updating the stored biography.</summary>
+public class UpdateBiographyHandler(IUserProfileRepository userProfileRepository)
+    : IRequestHandler<UpdateBiographyCommand>
+{
+    /// <exception cref="Domain.Exceptions.NotFoundException">
+    ///     Thrown when no user profile exists for the given user account.
+    /// </exception>
+    public Task Handle(UpdateBiographyCommand request, CancellationToken cancellationToken) =>
+        userProfileRepository.UpdateBiographyAsync(
+            request.UserAccountId,
+            request.Biography,
+            cancellationToken
+        );
+}

web/backend/Features/Features.Users/Commands/Profile/UpdateProfile/UpdateProfileCommand.cs

@@ -0,0 +1,19 @@
+using Features.Auth.Dtos;
+using MediatR;
+
+namespace Features.Auth.Commands.Profile.UpdateProfile;
+
+/// <summary>
+///     Updates the non-credential profile fields (first name, last name, date of birth) of the given
+///     user account.
+/// </summary>
+/// <param name="UserAccountId">
+///     The authenticated caller's own ID, extracted from the access token -- never bind this from
+///     client-supplied input.
+/// </param>
+public record UpdateProfileCommand(
+    Guid UserAccountId,
+    string FirstName,
+    string LastName,
+    DateTime DateOfBirth
+) : IRequest<UpdateProfilePayload>;

web/backend/Features/Features.Users/Commands/Profile/UpdateProfile/UpdateProfileHandler.cs

@@ -0,0 +1,40 @@
+using Domain.Exceptions;
+using Features.Auth.Dtos;
+using Features.Auth.Identity;
+using MediatR;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Commands.Profile.UpdateProfile;
+
+/// <summary>
+///     Handles <see cref="UpdateProfileCommand" /> via <see cref="UserManager{TUser}" />. First/last name
+///     and date of birth aren't tracked by any Identity-specific store interface, so the mutated
+///     <see cref="ApplicationUser" /> is saved directly through <see cref="UserManager{TUser}.UpdateAsync" />.
+/// </summary>
+public class UpdateProfileHandler(UserManager<ApplicationUser> userManager)
+    : IRequestHandler<UpdateProfileCommand, UpdateProfilePayload>
+{
+    /// <exception cref="NotFoundException">Thrown when the account does not exist.</exception>
+    /// <exception cref="ConflictException">Thrown when the update otherwise fails.</exception>
+    public async Task<UpdateProfilePayload> Handle(
+        UpdateProfileCommand request,
+        CancellationToken cancellationToken
+    )
+    {
+        ApplicationUser user =
+            await userManager.FindByIdAsync(request.UserAccountId.ToString())
+            ?? throw new NotFoundException("User account not found");
+
+        user.FirstName = request.FirstName;
+        user.LastName = request.LastName;
+        user.DateOfBirth = request.DateOfBirth;
+
+        IdentityResult result = await userManager.UpdateAsync(user);
+        if (!result.Succeeded)
+            throw new ConflictException(
+                string.Join("; ", result.Errors.Select(e => e.Description))
+            );
+
+        return new UpdateProfilePayload(user.Id, user.FirstName, user.LastName, user.DateOfBirth);
+    }
+}

web/backend/Features/Features.Users/Commands/Profile/UpdateProfile/UpdateProfileValidator.cs

@@ -0,0 +1,28 @@
+using FluentValidation;
+
+namespace Features.Auth.Commands.Profile.UpdateProfile;
+
+/// <summary>Validates <see cref="UpdateProfileCommand" />, mirroring the profile rules in <c>RegisterUserValidator</c>.</summary>
+public class UpdateProfileValidator : AbstractValidator<UpdateProfileCommand>
+{
+    public UpdateProfileValidator()
+    {
+        RuleFor(x => x.FirstName)
+            .NotEmpty()
+            .WithMessage("First name is required")
+            .MaximumLength(128)
+            .WithMessage("First name cannot exceed 128 characters");
+
+        RuleFor(x => x.LastName)
+            .NotEmpty()
+            .WithMessage("Last name is required")
+            .MaximumLength(128)
+            .WithMessage("Last name cannot exceed 128 characters");
+
+        RuleFor(x => x.DateOfBirth)
+            .NotEmpty()
+            .WithMessage("Date of birth is required")
+            .LessThan(DateTime.Today.AddYears(-19))
+            .WithMessage("You must be at least 19 years old");
+    }
+}

web/backend/Features/Features.Users/Commands/Profile/UploadAvatar/UploadAvatarCommand.cs

@@ -0,0 +1,7 @@
+using MediatR;
+using Microsoft.AspNetCore.Http;
+
+namespace Features.Auth.Commands.Profile.UploadAvatar;
+
+/// <summary>Uploads a new avatar photo for a user account, replacing any existing avatar.</summary>
+public record UploadAvatarCommand(Guid UserAccountId, IFormFile File) : IRequest<Guid>;

web/backend/Features/Features.Users/Commands/Profile/UploadAvatar/UploadAvatarHandler.cs

@@ -0,0 +1,42 @@
+using Domain.Entities;
+using Features.Auth.Repository;
+using Features.ImageUploads.Commands.UploadPhoto;
+using MediatR;
+
+namespace Features.Auth.Commands.Profile.UploadAvatar;
+
+/// <summary>
+///     Handles <see cref="UploadAvatarCommand" />: uploads the photo via <see cref="UploadPhotoCommand" />,
+///     then saves the <see cref="UserAvatar" /> record, replacing any existing avatar for the user.
+/// </summary>
+public class UploadAvatarHandler(IMediator mediator, IUserProfileRepository userProfileRepository)
+    : IRequestHandler<UploadAvatarCommand, Guid>
+{
+    public async Task<Guid> Handle(UploadAvatarCommand request, CancellationToken cancellationToken)
+    {
+        Guid photoId = await mediator.Send(
+            new UploadPhotoCommand(
+                request.UserAccountId,
+                $"avatars/{request.UserAccountId}",
+                request.File
+            ),
+            cancellationToken
+        );
+
+        Guid profileId = await userProfileRepository.GetProfileIdAsync(
+            request.UserAccountId,
+            cancellationToken
+        );
+
+        UserAvatar avatar = new()
+        {
+            UserAvatarId = Guid.NewGuid(),
+            UserProfileId = profileId,
+            PhotoId = photoId,
+        };
+
+        await userProfileRepository.SaveAvatarAsync(avatar, cancellationToken);
+
+        return photoId;
+    }
+}

web/backend/Features/Features.Users/Controllers/AuthController.cs

@@ -0,0 +1,247 @@
+using System.IdentityModel.Tokens.Jwt;
+using Domain.Exceptions;
+using Features.Auth.Commands.Account.DeleteAccount;
+using Features.Auth.Commands.Account.UpdateEmail;
+using Features.Auth.Commands.Account.UpdatePassword;
+using Features.Auth.Commands.Account.UpdateUsername;
+using Features.Auth.Commands.Authentication.ConfirmUser;
+using Features.Auth.Commands.Authentication.Login;
+using Features.Auth.Commands.Authentication.RefreshToken;
+using Features.Auth.Commands.Authentication.RegisterUser;
+using Features.Auth.Commands.Authentication.ResendConfirmationEmail;
+using Features.Auth.Commands.Profile.UpdateProfile;
+using Features.Auth.Dtos;
+using MediatR;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using Shared.Contracts;
+
+namespace Features.Auth.Controllers;
+
+/// <summary>
+///     Handles user authentication concerns: registration, login, email confirmation, token refresh, and
+///     self-service account management.
+/// </summary>
+/// <remarks>
+///     The controller is decorated with <c>[Authorize(AuthenticationSchemes = "JWT")]</c> by default, but most
+///     actions opt out via <c>[AllowAnonymous]</c> since they are entry points used before a caller holds a token.
+/// </remarks>
+[ApiController]
+[Route("api/[controller]")]
+[Authorize(AuthenticationSchemes = "JWT")]
+public class AuthController(IMediator mediator) : ControllerBase
+{
+    /// <summary>
+    ///     Extracts the authenticated caller's user ID from the validated access token's <c>sub</c> claim.
+    /// </summary>
+    /// <exception cref="UnauthorizedException">Thrown when the claim is missing or malformed.</exception>
+    private Guid GetAuthenticatedUserId()
+    {
+        string? userIdClaim = User.FindFirst(JwtRegisteredClaimNames.Sub)?.Value;
+        if (!Guid.TryParse(userIdClaim, out Guid userId))
+            throw new UnauthorizedException("Access token is missing a valid user ID claim");
+        return userId;
+    }
+
+    /// <summary>Registers a new user account.</summary>
+    /// <remarks>
+    ///     Anonymous access. Returns 201 Created with the new account's ID, username, and issued tokens.
+    ///     Returns 409 Conflict if the username or email is already taken.
+    /// </remarks>
+    [AllowAnonymous]
+    [HttpPost("register")]
+    public async Task<ActionResult<ResponseBody<RegistrationPayload>>> Register(
+        [FromBody] RegisterUserCommand command
+    )
+    {
+        RegistrationPayload payload = await mediator.Send(command);
+        return Created(
+            "/",
+            new ResponseBody<RegistrationPayload>
+            {
+                Message = "User registered successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Authenticates a user by username and password and issues a new access/refresh token pair.</summary>
+    /// <remarks>
+    ///     Anonymous access. Returns 200 OK with the tokens, or 401 Unauthorized if the credentials are invalid.
+    /// </remarks>
+    [AllowAnonymous]
+    [HttpPost("login")]
+    public async Task<ActionResult<ResponseBody<LoginPayload>>> Login(
+        [FromBody] LoginCommand command
+    )
+    {
+        LoginPayload payload = await mediator.Send(command);
+        return Ok(
+            new ResponseBody<LoginPayload>
+            {
+                Message = "Logged in successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Confirms a user account using a confirmation token.</summary>
+    /// <remarks>
+    ///     Requires a valid JWT bearer token (no <c>[AllowAnonymous]</c> override). Returns 200 OK on success,
+    ///     or 401 Unauthorized if <paramref name="token" /> is invalid or expired.
+    /// </remarks>
+    [HttpPost("confirm")]
+    public async Task<ActionResult<ResponseBody<ConfirmationPayload>>> Confirm(
+        [FromQuery] string token
+    )
+    {
+        ConfirmationPayload payload = await mediator.Send(new ConfirmUserCommand(token));
+        return Ok(
+            new ResponseBody<ConfirmationPayload>
+            {
+                Message = "User with ID " + payload.UserAccountId + " is confirmed.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Resends the account confirmation email for the given user, generating a fresh confirmation token.</summary>
+    /// <remarks>
+    ///     Requires a valid JWT bearer token (no <c>[AllowAnonymous]</c> override). Always returns 200 OK, even
+    ///     if <paramref name="userId" /> does not exist or the account is already confirmed, to avoid user
+    ///     enumeration.
+    /// </remarks>
+    [HttpPost("confirm/resend")]
+    public async Task<ActionResult<ResponseBody>> ResendConfirmation([FromQuery] Guid userId)
+    {
+        await mediator.Send(new ResendConfirmationEmailCommand(userId));
+        return Ok(new ResponseBody { Message = "confirmation email has been resent" });
+    }
+
+    /// <summary>Exchanges a valid refresh token for a new access/refresh token pair.</summary>
+    /// <remarks>
+    ///     Anonymous access. The refresh token is supplied via the <c>X-Refresh-Token</c> header, not the
+    ///     request body. Returns 200 OK with the new tokens, 400 Bad Request if the header is missing, or
+    ///     401 Unauthorized if the refresh token is invalid or expired.
+    /// </remarks>
+    [AllowAnonymous]
+    [HttpPost("refresh")]
+    public async Task<ActionResult<ResponseBody<LoginPayload>>> Refresh(
+        [FromHeader(Name = "X-Refresh-Token")] string? refreshToken
+    )
+    {
+        LoginPayload payload = await mediator.Send(
+            new RefreshTokenCommand(refreshToken ?? string.Empty)
+        );
+        return Ok(
+            new ResponseBody<LoginPayload>
+            {
+                Message = "Token refreshed successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Changes the authenticated user's username.</summary>
+    /// <remarks>Returns 200 OK with the updated username, or 409 Conflict if it is already taken.</remarks>
+    [HttpPatch("username")]
+    public async Task<ActionResult<ResponseBody<UpdateUsernamePayload>>> UpdateUsername(
+        [FromBody] UpdateUsernameRequest request
+    )
+    {
+        UpdateUsernamePayload payload = await mediator.Send(
+            new UpdateUsernameCommand(GetAuthenticatedUserId(), request.NewUsername)
+        );
+        return Ok(
+            new ResponseBody<UpdateUsernamePayload>
+            {
+                Message = "Username updated successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Changes the authenticated user's email address.</summary>
+    /// <remarks>
+    ///     Returns 200 OK with the updated (now unconfirmed) email address, or 409 Conflict if it is
+    ///     already in use. The caller should use <c>POST /api/auth/confirm/resend</c> to re-confirm.
+    /// </remarks>
+    [HttpPatch("email")]
+    public async Task<ActionResult<ResponseBody<UpdateEmailPayload>>> UpdateEmail(
+        [FromBody] UpdateEmailRequest request
+    )
+    {
+        UpdateEmailPayload payload = await mediator.Send(
+            new UpdateEmailCommand(GetAuthenticatedUserId(), request.NewEmail)
+        );
+        return Ok(
+            new ResponseBody<UpdateEmailPayload>
+            {
+                Message = "Email updated successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Changes the authenticated user's password.</summary>
+    /// <remarks>
+    ///     Returns 200 OK on success, or 401 Unauthorized if <c>CurrentPassword</c> does not match the
+    ///     account's current password.
+    /// </remarks>
+    [HttpPatch("password")]
+    public async Task<ActionResult<ResponseBody<UpdatePasswordPayload>>> UpdatePassword(
+        [FromBody] UpdatePasswordRequest request
+    )
+    {
+        UpdatePasswordPayload payload = await mediator.Send(
+            new UpdatePasswordCommand(
+                GetAuthenticatedUserId(),
+                request.CurrentPassword,
+                request.NewPassword
+            )
+        );
+        return Ok(
+            new ResponseBody<UpdatePasswordPayload>
+            {
+                Message = "Password updated successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Updates the authenticated user's profile fields (first name, last name, date of birth).</summary>
+    /// <remarks>Returns 200 OK with the updated profile.</remarks>
+    [HttpPatch("profile")]
+    public async Task<ActionResult<ResponseBody<UpdateProfilePayload>>> UpdateProfile(
+        [FromBody] UpdateProfileRequest request
+    )
+    {
+        UpdateProfilePayload payload = await mediator.Send(
+            new UpdateProfileCommand(
+                GetAuthenticatedUserId(),
+                request.FirstName,
+                request.LastName,
+                request.DateOfBirth
+            )
+        );
+        return Ok(
+            new ResponseBody<UpdateProfilePayload>
+            {
+                Message = "Profile updated successfully.",
+                Payload = payload,
+            }
+        );
+    }
+
+    /// <summary>Permanently deletes the authenticated user's account.</summary>
+    /// <remarks>
+    ///     Returns 200 OK on success, or 409 Conflict if the account still has associated posts, comments,
+    ///     photos, or follows.
+    /// </remarks>
+    [HttpDelete("account")]
+    public async Task<ActionResult<ResponseBody>> DeleteAccount()
+    {
+        await mediator.Send(new DeleteAccountCommand(GetAuthenticatedUserId()));
+        return Ok(new ResponseBody { Message = "Account deleted successfully." });
+    }
+}

web/backend/Features/Features.Users/Controllers/UserController.cs

@@ -0,0 +1,40 @@
+using Domain.Entities;
+using Domain.Exceptions;
+using Features.Auth.Queries.GetAllUsers;
+using Features.Auth.Queries.GetUserById;
+using MediatR;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Features.Auth.Controllers;
+
+/// <summary>
+///     Exposes read endpoints for user accounts.
+/// </summary>
+[ApiController]
+[Route("api/[controller]")]
+public class UserController(IMediator mediator) : ControllerBase
+{
+    /// <summary>Gets a page of user accounts, ordered by creation date descending.</summary>
+    /// <param name="limit"><c>null</c> for no limit.</param>
+    /// <param name="offset"><c>null</c> for no offset.</param>
+    [HttpGet]
+    public async Task<ActionResult<IEnumerable<UserAccount>>> GetAll(
+        [FromQuery] int? limit,
+        [FromQuery] int? offset
+    )
+    {
+        IEnumerable<UserAccount> users = await mediator.Send(new GetAllUsersQuery(limit, offset));
+        return Ok(users);
+    }
+
+    /// <summary>Gets the user account with the given ID.</summary>
+    /// <exception cref="NotFoundException">
+    /// Thrown when no user account exists with the given ID, resulting in a 404 response.
+    /// </exception>
+    [HttpGet("{id:guid}")]
+    public async Task<ActionResult<UserAccount>> GetById(Guid id)
+    {
+        UserAccount user = await mediator.Send(new GetUserByIdQuery(id));
+        return Ok(user);
+    }
+}

web/backend/Features/Features.Users/DependencyInjection/FeaturesUsersServiceCollectionExtensions.cs

@@ -0,0 +1,58 @@
+using Features.Auth.Identity;
+using Features.Auth.Repository;
+using Features.Auth.Services;
+using Infrastructure.PasswordHashing;
+using Microsoft.AspNetCore.Identity;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace Features.Users.DependencyInjection;
+
+/// <summary>Registers the services required by Features.Users with the dependency injection container.</summary>
+public static class FeaturesUsersServiceCollectionExtensions
+{
+    /// <summary>
+    ///     Adds <see cref="ITokenService" />, <see cref="IUserListRepository" />,
+    ///     <see cref="IUserProfileRepository" />, and ASP.NET Core Identity
+    ///     (<see cref="UserManager{TUser}" /> backed by <see cref="DapperUserStore" /> and
+    ///     <see cref="Argon2PasswordHasher" />) as scoped services.
+    /// </summary>
+    public static IServiceCollection AddFeaturesUsers(this IServiceCollection services)
+    {
+        services.AddScoped<ITokenService, TokenService>();
+        services.AddScoped<IPasswordInfrastructure, Argon2Infrastructure>();
+        services.AddScoped<IUserListRepository, UserListRepository>();
+        services.AddScoped<IUserProfileRepository, UserProfileRepository>();
+
+        // AddDefaultTokenProviders() is deliberately not called: it registers
+        // DataProtectorTokenProvider<TUser>, which UserManager's constructor resolves eagerly and which
+        // requires IDataProtectionProvider -- not registered in the plain-console-app DI containers this
+        // solution builds (e.g. Database.Seed). Identity's own token providers are unused here anyway;
+        // account confirmation keeps using its own JWT-based tokens (see ITokenService).
+        services.AddIdentityCore<ApplicationUser>(options =>
+        {
+            options.User.RequireUniqueEmail = true;
+
+            // Password/username complexity is already enforced by RegisterUserValidator
+            // (FluentValidation); disable Identity's own checks to avoid duplicated/drifting rules.
+            options.Password.RequireDigit = false;
+            options.Password.RequireLowercase = false;
+            options.Password.RequireUppercase = false;
+            options.Password.RequireNonAlphanumeric = false;
+            options.Password.RequiredLength = 1;
+        });
+
+        services.AddScoped<DapperUserStore>();
+        services.AddScoped<IUserStore<ApplicationUser>>(sp =>
+            sp.GetRequiredService<DapperUserStore>()
+        );
+        services.AddScoped<IUserEmailStore<ApplicationUser>>(sp =>
+            sp.GetRequiredService<DapperUserStore>()
+        );
+        services.AddScoped<IUserPasswordStore<ApplicationUser>>(sp =>
+            sp.GetRequiredService<DapperUserStore>()
+        );
+        services.AddScoped<IPasswordHasher<ApplicationUser>, Argon2PasswordHasher>();
+
+        return services;
+    }
+}

web/backend/Features/Features.Users/Dtos/AuthPayloads.cs

@@ -0,0 +1,66 @@
+namespace Features.Auth.Dtos;
+
+/// <summary>Payload returned to the client after a successful login or token refresh.</summary>
+public record LoginPayload(
+    Guid UserAccountId,
+    string Username,
+    string RefreshToken,
+    string AccessToken
+);
+
+/// <summary>Payload returned to the client after a successful registration.</summary>
+public record RegistrationPayload(
+    Guid UserAccountId,
+    string Username,
+    string RefreshToken,
+    string AccessToken,
+    bool ConfirmationEmailSent
+);
+
+/// <summary>Payload returned to the client after a user account's email has been confirmed.</summary>
+public record ConfirmationPayload(Guid UserAccountId, DateTime ConfirmedDate);
+
+/// <summary>Request body for changing the authenticated user's username.</summary>
+/// <param name="NewUsername">
+///     The desired username; must be 3-64 characters and contain only letters, numbers, dots,
+///     underscores, and hyphens.
+/// </param>
+public record UpdateUsernameRequest(string NewUsername);
+
+/// <summary>Payload returned to the client after a username change.</summary>
+public record UpdateUsernamePayload(Guid UserAccountId, string Username);
+
+/// <summary>Request body for changing the authenticated user's email address.</summary>
+/// <param name="NewEmail">The new email address; up to 128 characters and must be a valid email format.</param>
+public record UpdateEmailRequest(string NewEmail);
+
+/// <summary>
+///     Payload returned to the client after an email change. The new address is unconfirmed until the
+///     user completes the confirmation flow again.
+/// </summary>
+public record UpdateEmailPayload(Guid UserAccountId, string Email, bool EmailConfirmed);
+
+/// <summary>Request body for updating the authenticated user's profile fields.</summary>
+/// <param name="FirstName">The user's first name; up to 128 characters.</param>
+/// <param name="LastName">The user's last name; up to 128 characters.</param>
+/// <param name="DateOfBirth">The user's date of birth; the user must be at least 19 years old.</param>
+public record UpdateProfileRequest(string FirstName, string LastName, DateTime DateOfBirth);
+
+/// <summary>Payload returned to the client after a profile update.</summary>
+public record UpdateProfilePayload(
+    Guid UserAccountId,
+    string FirstName,
+    string LastName,
+    DateTime DateOfBirth
+);
+
+/// <summary>Request body for changing the authenticated user's password.</summary>
+/// <param name="CurrentPassword">The user's current plaintext password, verified before the change is applied.</param>
+/// <param name="NewPassword">
+///     The desired new plaintext password; must be at least 8 characters and contain an uppercase letter, a
+///     lowercase letter, a number, and a special character.
+/// </param>
+public record UpdatePasswordRequest(string CurrentPassword, string NewPassword);
+
+/// <summary>Payload returned to the client after a password change.</summary>
+public record UpdatePasswordPayload(Guid UserAccountId, DateTime ChangedAt);

web/backend/Features/Features.Users/Features.Users.csproj

@@ -0,0 +1,25 @@
+<Project Sdk="Microsoft.NET.Sdk">
+    <PropertyGroup>
+        <TargetFramework>net10.0</TargetFramework>
+        <ImplicitUsings>enable</ImplicitUsings>
+        <Nullable>enable</Nullable>
+
+        <RootNamespace>Features.Auth</RootNamespace>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <FrameworkReference Include="Microsoft.AspNetCore.App" />
+    </ItemGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\Domain\Domain.Entities\Domain.Entities.csproj" />
+        <ProjectReference Include="..\..\Domain\Domain.Exceptions\Domain.Exceptions.csproj" />
+        <ProjectReference Include="..\..\Infrastructure\Infrastructure.Configuration\Infrastructure.Configuration.csproj" />
+        <ProjectReference Include="..\..\Infrastructure\Infrastructure.Jwt\Infrastructure.Jwt.csproj" />
+        <ProjectReference Include="..\..\Infrastructure\Infrastructure.PasswordHashing\Infrastructure.PasswordHashing.csproj" />
+        <ProjectReference Include="..\..\Database\Database.Connection\Database.Connection.csproj" />
+        <ProjectReference Include="..\Features.PhotoUpload\Features.PhotoUpload.csproj" />
+        <ProjectReference Include="..\..\Shared\Shared.Contracts\Shared.Contracts.csproj" />
+        <ProjectReference Include="..\..\Shared\Shared.Application\Shared.Application.csproj" />
+    </ItemGroup>
+</Project>

web/backend/Features/Features.Users/Identity/ApplicationUser.cs

@@ -0,0 +1,22 @@
+namespace Features.Auth.Identity;
+
+/// <summary>
+///     The user type driving <see cref="Microsoft.AspNetCore.Identity.UserManager{TUser}" /> for
+///     Features.Users. A plain POCO (not <c>IdentityUser&lt;TKey&gt;</c>) backed by <see cref="DapperUserStore" />
+///     rather than EF Core, matching the rest of the solution's Dapper-only persistence.
+/// </summary>
+public sealed class ApplicationUser
+{
+    public Guid Id { get; set; }
+    public string UserName { get; set; } = string.Empty;
+    public string? NormalizedUserName { get; set; }
+    public string Email { get; set; } = string.Empty;
+    public string? NormalizedEmail { get; set; }
+    public bool EmailConfirmed { get; set; }
+
+    /// <summary>The current Argon2 hash, or <see langword="null" /> if the account has no password set.</summary>
+    public string? PasswordHash { get; set; }
+    public string FirstName { get; set; } = string.Empty;
+    public string LastName { get; set; } = string.Empty;
+    public DateTime DateOfBirth { get; set; }
+}

web/backend/Features/Features.Users/Identity/Argon2PasswordHasher.cs

@@ -0,0 +1,28 @@
+using Infrastructure.PasswordHashing;
+using Microsoft.AspNetCore.Identity;
+
+namespace Features.Auth.Identity;
+
+/// <summary>Adapts <see cref="IPasswordInfrastructure" />'s Argon2 hashing to <see cref="IPasswordHasher{TUser}" />.</summary>
+public sealed class Argon2PasswordHasher(IPasswordInfrastructure passwordInfrastructure)
+    : IPasswordHasher<ApplicationUser>
+{
+    /// <inheritdoc />
+    public string HashPassword(ApplicationUser user, string password) =>
+        passwordInfrastructure.Hash(password);
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     Never returns <see cref="PasswordVerificationResult.SuccessRehashNeeded" />: Argon2 parameters are
+    ///     fixed by <see cref="IPasswordInfrastructure" />, so <see cref="UserManager{TUser}" />'s automatic
+    ///     rehash-on-verify path never triggers.
+    /// </remarks>
+    public PasswordVerificationResult VerifyHashedPassword(
+        ApplicationUser user,
+        string hashedPassword,
+        string providedPassword
+    ) =>
+        passwordInfrastructure.Verify(providedPassword, hashedPassword)
+            ? PasswordVerificationResult.Success
+            : PasswordVerificationResult.Failed;
+}

web/backend/Features/Features.Users/Identity/DapperUserStore.cs

@@ -0,0 +1,511 @@
+using System.Data.Common;
+using Dapper;
+using Database.Connection;
+using Microsoft.AspNetCore.Identity;
+using Microsoft.Data.SqlClient;
+
+namespace Features.Auth.Identity;
+
+/// <summary>
+///     Dapper-based implementation of the ASP.NET Core Identity store interfaces consumed by
+///     <see cref="UserManager{TUser}" />, persisting against the existing <c>dbo.UserAccount</c>,
+///     <c>dbo.UserCredential</c>, and <c>dbo.UserVerification</c> tables. No EF Core is used, and no schema
+///     changes were required: normalized name/email are computed on the fly rather than persisted (the
+///     existing unique indexes are already case-insensitive under SQL Server's default collation).
+/// </summary>
+public sealed class DapperUserStore(ISqlConnectionFactory connectionFactory)
+    : DapperRepository(connectionFactory),
+        IUserStore<ApplicationUser>,
+        IUserPasswordStore<ApplicationUser>,
+        IUserEmailStore<ApplicationUser>
+{
+    private const string SelectUserSql = """
+        SELECT UserAccountID AS Id, Username AS UserName, FirstName, LastName, Email, DateOfBirth
+        FROM dbo.UserAccount
+        """;
+
+    /// <remarks>No unmanaged resources to release; each method opens and disposes its own connection.</remarks>
+    public void Dispose() { }
+
+    /// <inheritdoc />
+    public Task<string> GetUserIdAsync(ApplicationUser user, CancellationToken cancellationToken) =>
+        Task.FromResult(user.Id.ToString());
+
+    /// <inheritdoc />
+    public Task<string?> GetUserNameAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    ) => Task.FromResult<string?>(user.UserName);
+
+    /// <inheritdoc />
+    public Task SetUserNameAsync(
+        ApplicationUser user,
+        string? userName,
+        CancellationToken cancellationToken
+    )
+    {
+        user.UserName = userName ?? string.Empty;
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public Task<string?> GetNormalizedUserNameAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    ) => Task.FromResult(user.NormalizedUserName);
+
+    /// <inheritdoc />
+    public Task SetNormalizedUserNameAsync(
+        ApplicationUser user,
+        string? normalizedName,
+        CancellationToken cancellationToken
+    )
+    {
+        user.NormalizedUserName = normalizedName;
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     Inserts the account and its initial credential within a single database transaction, mirroring the
+    ///     previous <c>AuthRepository.RegisterUserAsync</c> behavior. <see cref="UserManager{TUser}" /> already
+    ///     checks username/email uniqueness before calling this method, so the duplicate-key branch here only
+    ///     guards against a genuine race between two concurrent registrations.
+    /// </remarks>
+    public async Task<IdentityResult> CreateAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+        await using DbTransaction transaction = await connection.BeginTransactionAsync(
+            cancellationToken
+        );
+
+        try
+        {
+            Guid userAccountId = await connection.ExecuteScalarAsync<Guid>(
+                new CommandDefinition(
+                    """
+                    INSERT INTO dbo.UserAccount (Username, FirstName, LastName, DateOfBirth, Email)
+                    OUTPUT INSERTED.UserAccountID
+                    VALUES (@UserName, @FirstName, @LastName, @DateOfBirth, @Email);
+                    """,
+                    new
+                    {
+                        user.UserName,
+                        user.FirstName,
+                        user.LastName,
+                        user.DateOfBirth,
+                        user.Email,
+                    },
+                    transaction,
+                    cancellationToken: cancellationToken
+                )
+            );
+
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    """
+                    INSERT INTO dbo.UserCredential (UserAccountId, Hash)
+                    VALUES (@UserAccountId, @Hash);
+                    """,
+                    new { UserAccountId = userAccountId, Hash = user.PasswordHash },
+                    transaction,
+                    cancellationToken: cancellationToken
+                )
+            );
+
+            await transaction.CommitAsync(cancellationToken);
+            user.Id = userAccountId;
+        }
+        catch (SqlException ex) when (IsDuplicateKeyViolation(ex))
+        {
+            await transaction.RollbackAsync(cancellationToken);
+            return IdentityResult.Failed(
+                new IdentityError
+                {
+                    Code = "DuplicateUserName",
+                    Description = "Username or email already exists.",
+                }
+            );
+        }
+        catch
+        {
+            await transaction.RollbackAsync(cancellationToken);
+            throw;
+        }
+
+        return IdentityResult.Success;
+    }
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     Persists profile field changes and keeps <c>dbo.UserVerification</c> in sync with
+    ///     <see cref="ApplicationUser.EmailConfirmed" />: a row is inserted (idempotently, matching the
+    ///     previous <c>AuthRepository.ConfirmUserAccountAsync</c> behavior) when
+    ///     <see langword="true" />, and removed when <see langword="false" /> -- notably after
+    ///     <see cref="UserManager{TUser}.SetEmailAsync" /> resets confirmation on an email change.
+    /// </remarks>
+    public async Task<IdentityResult> UpdateAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+
+        await connection.ExecuteAsync(
+            new CommandDefinition(
+                """
+                UPDATE dbo.UserAccount
+                SET Username = @UserName, FirstName = @FirstName, LastName = @LastName,
+                    Email = @Email, DateOfBirth = @DateOfBirth, UpdatedAt = GETDATE()
+                WHERE UserAccountID = @Id
+                """,
+                new
+                {
+                    user.Id,
+                    user.UserName,
+                    user.FirstName,
+                    user.LastName,
+                    user.Email,
+                    user.DateOfBirth,
+                },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        if (user.EmailConfirmed)
+            await EnsureVerificationRowAsync(connection, user.Id, cancellationToken);
+        else
+            await RemoveVerificationRowAsync(connection, user.Id, cancellationToken);
+
+        return IdentityResult.Success;
+    }
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     A plain <c>DELETE</c> against <c>dbo.UserAccount</c>: its foreign keys from
+    ///     <c>dbo.UserCredential</c>, <c>dbo.UserVerification</c>, and <c>dbo.UserProfile</c> cascade
+    ///     (<c>dbo.UserAvatar</c> cascades transitively through <c>dbo.UserProfile</c>), so no manual
+    ///     child cleanup is needed. Other tables (posts, comments, photos, follows) reference the
+    ///     account with <c>ON DELETE NO ACTION</c> by design; deleting an account that still has any of
+    ///     those fails with a foreign key violation, which is surfaced as a failed
+    ///     <see cref="IdentityResult" /> rather than an unhandled <see cref="SqlException" />.
+    /// </remarks>
+    public async Task<IdentityResult> DeleteAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+
+        try
+        {
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    "DELETE FROM dbo.UserAccount WHERE UserAccountID = @Id",
+                    new { user.Id },
+                    cancellationToken: cancellationToken
+                )
+            );
+        }
+        catch (SqlException ex) when (IsForeignKeyViolation(ex))
+        {
+            return IdentityResult.Failed(
+                new IdentityError
+                {
+                    Code = "AccountHasDependentRecords",
+                    Description =
+                        "Account cannot be deleted because other records still reference it.",
+                }
+            );
+        }
+
+        return IdentityResult.Success;
+    }
+
+    /// <inheritdoc />
+    public async Task<ApplicationUser?> FindByIdAsync(
+        string userId,
+        CancellationToken cancellationToken
+    )
+    {
+        if (!Guid.TryParse(userId, out Guid id))
+            return null;
+
+        await using DbConnection connection = await CreateConnection();
+        ApplicationUser? user = await connection.QueryFirstOrDefaultAsync<ApplicationUser>(
+            new CommandDefinition(
+                $"{SelectUserSql} WHERE UserAccountID = @Id",
+                new { Id = id },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        if (user != null)
+            await HydrateAsync(connection, user, cancellationToken);
+
+        return user;
+    }
+
+    /// <inheritdoc />
+    public async Task<ApplicationUser?> FindByNameAsync(
+        string normalizedUserName,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+        ApplicationUser? user = await connection.QueryFirstOrDefaultAsync<ApplicationUser>(
+            new CommandDefinition(
+                $"{SelectUserSql} WHERE Username = @UserName",
+                new { UserName = normalizedUserName },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        if (user != null)
+            await HydrateAsync(connection, user, cancellationToken);
+
+        return user;
+    }
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     For an existing account (<see cref="ApplicationUser.Id" /> already assigned), rotates the
+    ///     credential transactionally -- revoking the previous <c>dbo.UserCredential</c> row(s) and inserting
+    ///     the new hash -- mirroring the previous <c>AuthRepository.RotateCredentialAsync</c> behavior. During
+    ///     registration <see cref="UserManager{TUser}" /> calls this before the account has an ID (i.e. before
+    ///     <see cref="CreateAsync" /> runs); in that case only the in-memory hash is set, and
+    ///     <see cref="CreateAsync" /> writes the initial credential itself as part of its own transaction.
+    /// </remarks>
+    public async Task SetPasswordHashAsync(
+        ApplicationUser user,
+        string? passwordHash,
+        CancellationToken cancellationToken
+    )
+    {
+        string? previousHash = user.PasswordHash;
+        user.PasswordHash = passwordHash;
+
+        if (user.Id == Guid.Empty || passwordHash == null || passwordHash == previousHash)
+            return;
+
+        await using DbConnection connection = await CreateConnection();
+        await using DbTransaction transaction = await connection.BeginTransactionAsync(
+            cancellationToken
+        );
+
+        try
+        {
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    """
+                    UPDATE dbo.UserCredential
+                    SET IsRevoked = 1, RevokedAt = GETDATE()
+                    WHERE UserAccountId = @UserAccountId AND IsRevoked = 0
+                    """,
+                    new { UserAccountId = user.Id },
+                    transaction,
+                    cancellationToken: cancellationToken
+                )
+            );
+
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    """
+                    INSERT INTO dbo.UserCredential (UserAccountId, Hash)
+                    VALUES (@UserAccountId, @Hash);
+                    """,
+                    new { UserAccountId = user.Id, Hash = passwordHash },
+                    transaction,
+                    cancellationToken: cancellationToken
+                )
+            );
+
+            await transaction.CommitAsync(cancellationToken);
+        }
+        catch
+        {
+            await transaction.RollbackAsync(cancellationToken);
+            throw;
+        }
+    }
+
+    /// <inheritdoc />
+    public Task<string?> GetPasswordHashAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    ) => Task.FromResult(user.PasswordHash);
+
+    /// <inheritdoc />
+    public Task<bool> HasPasswordAsync(ApplicationUser user, CancellationToken cancellationToken) =>
+        Task.FromResult(user.PasswordHash != null);
+
+    /// <inheritdoc />
+    public Task SetEmailAsync(
+        ApplicationUser user,
+        string? email,
+        CancellationToken cancellationToken
+    )
+    {
+        user.Email = email ?? string.Empty;
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public Task<string?> GetEmailAsync(ApplicationUser user, CancellationToken cancellationToken) =>
+        Task.FromResult<string?>(user.Email);
+
+    /// <inheritdoc />
+    public Task<bool> GetEmailConfirmedAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    ) => Task.FromResult(user.EmailConfirmed);
+
+    /// <inheritdoc />
+    public Task SetEmailConfirmedAsync(
+        ApplicationUser user,
+        bool confirmed,
+        CancellationToken cancellationToken
+    )
+    {
+        user.EmailConfirmed = confirmed;
+        return Task.CompletedTask;
+    }
+
+    /// <inheritdoc />
+    public async Task<ApplicationUser?> FindByEmailAsync(
+        string normalizedEmail,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+        ApplicationUser? user = await connection.QueryFirstOrDefaultAsync<ApplicationUser>(
+            new CommandDefinition(
+                $"{SelectUserSql} WHERE Email = @Email",
+                new { Email = normalizedEmail },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        if (user != null)
+            await HydrateAsync(connection, user, cancellationToken);
+
+        return user;
+    }
+
+    /// <inheritdoc />
+    public Task<string?> GetNormalizedEmailAsync(
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    ) => Task.FromResult(user.NormalizedEmail);
+
+    /// <inheritdoc />
+    public Task SetNormalizedEmailAsync(
+        ApplicationUser user,
+        string? normalizedEmail,
+        CancellationToken cancellationToken
+    )
+    {
+        user.NormalizedEmail = normalizedEmail;
+        return Task.CompletedTask;
+    }
+
+    /// <summary>Loads the active credential hash and verification status onto a freshly queried user.</summary>
+    private static async Task HydrateAsync(
+        DbConnection connection,
+        ApplicationUser user,
+        CancellationToken cancellationToken
+    )
+    {
+        user.PasswordHash = await connection.ExecuteScalarAsync<string?>(
+            new CommandDefinition(
+                """
+                SELECT Hash
+                FROM dbo.UserCredential
+                WHERE UserAccountId = @UserAccountId AND IsRevoked = 0
+                """,
+                new { UserAccountId = user.Id },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        int? verified = await connection.ExecuteScalarAsync<int?>(
+            new CommandDefinition(
+                """
+                SELECT TOP 1 1
+                FROM dbo.UserVerification
+                WHERE UserAccountID = @UserAccountId
+                """,
+                new { UserAccountId = user.Id },
+                cancellationToken: cancellationToken
+            )
+        );
+        user.EmailConfirmed = verified.HasValue;
+    }
+
+    /// <remarks>
+    ///     If a concurrent request verifies the same user first, the resulting duplicate-key SQL exception
+    ///     (error 2601/2627) is swallowed to keep the operation idempotent.
+    /// </remarks>
+    private static async Task EnsureVerificationRowAsync(
+        DbConnection connection,
+        Guid userAccountId,
+        CancellationToken cancellationToken
+    )
+    {
+        int? alreadyVerified = await connection.ExecuteScalarAsync<int?>(
+            new CommandDefinition(
+                """
+                SELECT TOP 1 1
+                FROM dbo.UserVerification
+                WHERE UserAccountID = @UserAccountId
+                """,
+                new { UserAccountId = userAccountId },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        if (alreadyVerified.HasValue)
+            return;
+
+        try
+        {
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    """
+                    INSERT INTO dbo.UserVerification (UserAccountId, VerificationDateTime)
+                    VALUES (@UserAccountId, GETDATE())
+                    """,
+                    new { UserAccountId = userAccountId },
+                    cancellationToken: cancellationToken
+                )
+            );
+        }
+        catch (SqlException ex) when (IsDuplicateKeyViolation(ex))
+        {
+            // A concurrent request verified this user first. Keep behavior idempotent.
+        }
+    }
+
+    /// <summary>Removes the <c>dbo.UserVerification</c> row for a user, if one exists.</summary>
+    private static Task RemoveVerificationRowAsync(
+        DbConnection connection,
+        Guid userAccountId,
+        CancellationToken cancellationToken
+    ) =>
+        connection.ExecuteAsync(
+            new CommandDefinition(
+                "DELETE FROM dbo.UserVerification WHERE UserAccountID = @UserAccountId",
+                new { UserAccountId = userAccountId },
+                cancellationToken: cancellationToken
+            )
+        );
+
+    /// <summary>Determines whether a <see cref="SqlException" /> is a duplicate key violation (SQL Server error 2601 or 2627).</summary>
+    private static bool IsDuplicateKeyViolation(SqlException ex) => ex.Number is 2601 or 2627;
+
+    /// <summary>Determines whether a <see cref="SqlException" /> is a foreign key constraint violation (SQL Server error 547).</summary>
+    private static bool IsForeignKeyViolation(SqlException ex) => ex.Number == 547;
+}

web/backend/Features/Features.Users/Identity/UserAccountExtensions.cs

@@ -0,0 +1,23 @@
+using Domain.Entities;
+
+namespace Features.Auth.Identity;
+
+/// <summary>
+///     Converts the persistence-agnostic <see cref="UserAccount" /> domain entity into the
+///     <see cref="ApplicationUser" /> shape required by <see cref="Microsoft.AspNetCore.Identity.UserManager{TUser}" />.
+///     Kept here, in Features.Users, rather than on <see cref="UserAccount" /> itself so the domain layer has
+///     no dependency on ASP.NET Core Identity.
+/// </summary>
+public static class UserAccountExtensions
+{
+    public static ApplicationUser ToApplicationUser(this UserAccount userAccount) =>
+        new()
+        {
+            Id = userAccount.UserAccountId,
+            UserName = userAccount.Username,
+            Email = userAccount.Email,
+            FirstName = userAccount.FirstName,
+            LastName = userAccount.LastName,
+            DateOfBirth = userAccount.DateOfBirth,
+        };
+}

web/backend/Features/Features.Users/Queries/GetAllUsers/GetAllUsersHandler.cs

@@ -0,0 +1,17 @@
+using Domain.Entities;
+using Features.Auth.Repository;
+using MediatR;
+
+namespace Features.Auth.Queries.GetAllUsers;
+
+public class GetAllUsersHandler(IUserListRepository repository)
+    : IRequestHandler<GetAllUsersQuery, IEnumerable<UserAccount>>
+{
+    public Task<IEnumerable<UserAccount>> Handle(
+        GetAllUsersQuery request,
+        CancellationToken cancellationToken
+    )
+    {
+        return repository.GetAllAsync(request.Limit, request.Offset);
+    }
+}

web/backend/Features/Features.Users/Queries/GetAllUsers/GetAllUsersQuery.cs

@@ -0,0 +1,11 @@
+using Domain.Entities;
+using MediatR;
+
+namespace Features.Auth.Queries.GetAllUsers;
+
+/// <summary>
+///     Requests a page of user accounts, ordered by creation date descending.
+/// </summary>
+/// <param name="Limit"><c>null</c> for no limit.</param>
+/// <param name="Offset"><c>null</c> for no offset.</param>
+public record GetAllUsersQuery(int? Limit, int? Offset) : IRequest<IEnumerable<UserAccount>>;

web/backend/Features/Features.Users/Queries/GetUserById/GetUserByIdHandler.cs

@@ -0,0 +1,22 @@
+using Domain.Entities;
+using Domain.Exceptions;
+using Features.Auth.Repository;
+using MediatR;
+
+namespace Features.Auth.Queries.GetUserById;
+
+public class GetUserByIdHandler(IUserListRepository repository)
+    : IRequestHandler<GetUserByIdQuery, UserAccount>
+{
+    /// <exception cref="NotFoundException">Thrown when no user account exists with the given ID.</exception>
+    public async Task<UserAccount> Handle(
+        GetUserByIdQuery request,
+        CancellationToken cancellationToken
+    )
+    {
+        UserAccount? user = await repository.GetByIdAsync(request.UserAccountId);
+        if (user is null)
+            throw new NotFoundException($"User with ID {request.UserAccountId} not found");
+        return user;
+    }
+}

web/backend/Features/Features.Users/Queries/GetUserById/GetUserByIdQuery.cs

@@ -0,0 +1,6 @@
+using Domain.Entities;
+using MediatR;
+
+namespace Features.Auth.Queries.GetUserById;
+
+public record GetUserByIdQuery(Guid UserAccountId) : IRequest<UserAccount>;

web/backend/Features/Features.Users/Repository/IUserListRepository.cs

@@ -0,0 +1,21 @@
+using Domain.Entities;
+
+namespace Features.Auth.Repository;
+
+/// <summary>
+///     Read access for user account listing. Everything else on user accounts (lookup by
+///     username/email, create/update/delete) already goes through
+///     <see cref="Microsoft.AspNetCore.Identity.UserManager{TUser}" />; this repository only covers
+///     what <c>IUserStore</c> has no equivalent for: fetching by ID with full audit fields, and
+///     paginated listing.
+/// </summary>
+public interface IUserListRepository
+{
+    /// <summary>Returns <c>null</c> if no user account exists with the given ID.</summary>
+    Task<UserAccount?> GetByIdAsync(Guid id);
+
+    /// <summary>Returns user accounts ordered by creation date descending.</summary>
+    /// <param name="limit"><c>null</c> for no limit.</param>
+    /// <param name="offset"><c>null</c> for no offset.</param>
+    Task<IEnumerable<UserAccount>> GetAllAsync(int? limit, int? offset);
+}

web/backend/Features/Features.Users/Repository/IUserProfileRepository.cs

@@ -0,0 +1,41 @@
+using Domain.Entities;
+
+namespace Features.Auth.Repository;
+
+/// <summary>
+///     Repository for user profile records and their avatars.
+/// </summary>
+public interface IUserProfileRepository
+{
+    /// <summary>
+    ///     Creates a new user profile for <paramref name="userAccountId" /> with the given
+    ///     <paramref name="biography" /> and returns its <c>UserProfileID</c>.
+    /// </summary>
+    Task<Guid> CreateProfileAsync(
+        Guid userAccountId,
+        string biography,
+        CancellationToken cancellationToken
+    );
+
+    /// <summary>
+    ///     Returns the <c>UserProfileID</c> for <paramref name="userAccountId" />
+    /// </summary>
+    Task<Guid> GetProfileIdAsync(Guid userAccountId, CancellationToken cancellationToken);
+
+    /// <summary>
+    ///     Updates the biography of the user profile belonging to <paramref name="userAccountId" />.
+    /// </summary>
+    /// <exception cref="Domain.Exceptions.NotFoundException">
+    ///     Thrown when no user profile exists for <paramref name="userAccountId" />.
+    /// </exception>
+    Task UpdateBiographyAsync(
+        Guid userAccountId,
+        string biography,
+        CancellationToken cancellationToken
+    );
+
+    /// <summary>
+    ///     Persists <paramref name="avatar" />, replacing any existing avatar for the same user profile.
+    /// </summary>
+    Task SaveAvatarAsync(UserAvatar avatar, CancellationToken cancellationToken);
+}

web/backend/Features/Features.Users/Repository/UserListRepository.cs

@@ -0,0 +1,50 @@
+using System.Data.Common;
+using Dapper;
+using Database.Connection;
+using Domain.Entities;
+
+namespace Features.Auth.Repository;
+
+/// <summary>
+///     Dapper-based implementation of <see cref="IUserListRepository" />.
+/// </summary>
+public class UserListRepository(ISqlConnectionFactory connectionFactory)
+    : DapperRepository(connectionFactory),
+        IUserListRepository
+{
+    /// <inheritdoc />
+    public async Task<UserAccount?> GetByIdAsync(Guid id)
+    {
+        await using DbConnection connection = await CreateConnection();
+        return await connection.QueryFirstOrDefaultAsync<UserAccount>(
+            """
+            SELECT 
+                UserAccountID, 
+                Username, 
+                FirstName, LastName, Email, CreatedAt, UpdatedAt, DateOfBirth, RowVersion
+            FROM dbo.UserAccount
+            WHERE UserAccountID = @UserAccountId
+            """,
+            new { UserAccountId = id }
+        );
+    }
+
+    /// <inheritdoc />
+    /// <remarks>
+    ///     Always applies pagination via <c>OFFSET</c>/<c>FETCH</c>, ordered by creation date descending.
+    ///     A <c>null</c> <paramref name="limit" />/<paramref name="offset" /> is treated as "no limit"/"no offset".
+    /// </remarks>
+    public async Task<IEnumerable<UserAccount>> GetAllAsync(int? limit, int? offset)
+    {
+        await using DbConnection connection = await CreateConnection();
+        return await connection.QueryAsync<UserAccount>(
+            """
+            SELECT UserAccountID, Username, FirstName, LastName, Email, CreatedAt, UpdatedAt, DateOfBirth, RowVersion
+            FROM dbo.UserAccount
+            ORDER BY CreatedAt DESC
+            OFFSET @Offset ROWS FETCH NEXT @Limit ROWS ONLY
+            """,
+            new { Offset = offset ?? 0, Limit = limit ?? int.MaxValue }
+        );
+    }
+}

web/backend/Features/Features.Users/Repository/UserProfileRepository.cs

@@ -0,0 +1,139 @@
+using System.Data.Common;
+using Dapper;
+using Database.Connection;
+using Domain.Entities;
+using Domain.Exceptions;
+
+namespace Features.Auth.Repository;
+
+/// <summary>
+///     Dapper-based implementation of <see cref="IUserProfileRepository" />.
+/// </summary>
+public class UserProfileRepository(ISqlConnectionFactory connectionFactory)
+    : DapperRepository(connectionFactory),
+        IUserProfileRepository
+{
+    /// <inheritdoc />
+    public async Task<Guid> CreateProfileAsync(
+        Guid userAccountId,
+        string biography,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+
+        return await connection.ExecuteScalarAsync<Guid>(
+            new CommandDefinition(
+                """
+                INSERT INTO dbo.UserProfile (UserAccountID, Biography)
+                OUTPUT INSERTED.UserProfileID
+                VALUES (@UserAccountId, @Biography)
+                """,
+                new { UserAccountId = userAccountId, Biography = biography },
+                cancellationToken: cancellationToken
+            )
+        );
+    }
+
+    /// <inheritdoc />
+    public async Task<Guid> GetProfileIdAsync(
+        Guid userAccountId,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+
+        Guid? userProfileId = await connection.ExecuteScalarAsync<Guid?>(
+            new CommandDefinition(
+                """
+                SELECT UserProfileID
+                FROM dbo.UserProfile
+                WHERE UserAccountID = @UserAccountId
+                """,
+                new { UserAccountId = userAccountId },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        return userProfileId
+            ?? throw new NotFoundException(
+                $"No user profile found for user account ID {userAccountId}"
+            );
+    }
+
+    /// <inheritdoc />
+    public async Task UpdateBiographyAsync(
+        Guid userAccountId,
+        string biography,
+        CancellationToken cancellationToken
+    )
+    {
+        await using DbConnection connection = await CreateConnection();
+
+        int updatedRows = await connection.ExecuteAsync(
+            new CommandDefinition(
+                """
+                UPDATE dbo.UserProfile
+                SET Biography = @Biography
+                WHERE UserAccountID = @UserAccountId
+                """,
+                new { UserAccountId = userAccountId, Biography = biography },
+                cancellationToken: cancellationToken
+            )
+        );
+
+        if (updatedRows == 0)
+            throw new NotFoundException(
+                $"No user profile found for user account ID {userAccountId}"
+            );
+    }
+
+    /// <inheritdoc />
+    public async Task SaveAvatarAsync(UserAvatar avatar, CancellationToken cancellationToken)
+    {
+        await using DbConnection connection = await CreateConnection();
+        await using DbTransaction transaction = await connection.BeginTransactionAsync(
+            cancellationToken
+        );
+
+        try
+        {
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    """
+                    UPDATE dbo.UserAvatar
+                    SET ValidTo = SYSUTCDATETIME()
+                    WHERE UserProfileID = @UserProfileId AND ValidTo IS NULL
+                    """,
+                    new { avatar.UserProfileId },
+                    transaction: transaction,
+                    cancellationToken: cancellationToken
+                )
+            );
+
+            await connection.ExecuteAsync(
+                new CommandDefinition(
+                    """
+                    INSERT INTO dbo.UserAvatar (UserAvatarID, UserProfileID, PhotoID)
+                    VALUES (@UserAvatarId, @UserProfileId, @PhotoId)
+                    """,
+                    new
+                    {
+                        avatar.UserAvatarId,
+                        avatar.UserProfileId,
+                        avatar.PhotoId,
+                    },
+                    transaction: transaction,
+                    cancellationToken: cancellationToken
+                )
+            );
+
+            await transaction.CommitAsync(cancellationToken);
+        }
+        catch
+        {
+            await RollbackQuietlyAsync(transaction);
+            throw;
+        }
+    }
+}

web/backend/Features/Features.Users/Services/ITokenService.cs

@@ -0,0 +1,87 @@
+using System.Security.Claims;
+
+namespace Features.Auth.Services;
+
+/// <summary>
+///     Identifies the kind of token being generated or validated.
+/// </summary>
+public enum TokenType
+{
+    /// <summary>A short-lived token used to authorize API requests.</summary>
+    AccessToken,
+
+    /// <summary>A long-lived token used to obtain new access tokens.</summary>
+    RefreshToken,
+
+    /// <summary>A short-lived token used to confirm a user's email/account.</summary>
+    ConfirmationToken,
+}
+
+/// <summary>Represents the result of successfully validating a token.</summary>
+public record ValidatedToken(Guid UserId, string Username, ClaimsPrincipal Principal);
+
+/// <summary>Represents the result of refreshing a user's session.</summary>
+public record RefreshTokenResult(
+    Guid UserId,
+    string Username,
+    string RefreshToken,
+    string AccessToken
+);
+
+/// <summary>
+///     Defines the expiration windows, in hours, for each type of token issued by <see cref="ITokenService" />.
+/// </summary>
+public static class TokenServiceExpirationHours
+{
+    /// <summary>1 hour.</summary>
+    public const double AccessTokenHours = 1;
+
+    /// <summary>21 days.</summary>
+    public const double RefreshTokenHours = 504;
+
+    /// <summary>30 minutes.</summary>
+    public const double ConfirmationTokenHours = 0.5;
+}
+
+/// <summary>
+///     Defines operations for generating and validating JWTs used for access, refresh, and account confirmation.
+/// </summary>
+public interface ITokenService
+{
+    /// <summary>
+    ///     Generates a signed access token for the given user, expiring after
+    ///     <see cref="TokenServiceExpirationHours.AccessTokenHours" /> hours.
+    /// </summary>
+    string GenerateAccessToken(Guid userId, string username);
+
+    /// <summary>
+    ///     Generates a signed refresh token for the given user, expiring after
+    ///     <see cref="TokenServiceExpirationHours.RefreshTokenHours" /> hours.
+    /// </summary>
+    string GenerateRefreshToken(Guid userId, string username);
+
+    /// <summary>
+    ///     Generates a signed confirmation token for the given user, expiring after
+    ///     <see cref="TokenServiceExpirationHours.ConfirmationTokenHours" /> hours.
+    /// </summary>
+    string GenerateConfirmationToken(Guid userId, string username);
+
+    /// <summary>Validates a refresh token's signature and expiration and extracts the caller's identity.</summary>
+    /// <exception cref="Domain.Exceptions.UnauthorizedException">
+    ///     Thrown when the token is missing required claims, has a malformed user ID, or otherwise fails validation.
+    /// </exception>
+    Task<ValidatedToken> ValidateRefreshTokenAsync(string token);
+
+    /// <summary>Validates a confirmation token's signature and expiration and extracts the caller's identity.</summary>
+    /// <exception cref="Domain.Exceptions.UnauthorizedException">
+    ///     Thrown when the token is missing required claims, has a malformed user ID, or otherwise fails validation.
+    /// </exception>
+    Task<ValidatedToken> ValidateConfirmationTokenAsync(string token);
+
+    /// <summary>Validates a refresh token and issues a new access/refresh token pair for the associated user.</summary>
+    /// <exception cref="Domain.Exceptions.UnauthorizedException">
+    ///     Thrown when the refresh token is invalid or expired, or when the user account it refers to no
+    ///     longer exists.
+    /// </exception>
+    Task<RefreshTokenResult> RefreshTokenAsync(string refreshTokenString);
+}

web/backend/Features/Features.Users/Services/TokenService.cs

@@ -0,0 +1,150 @@
+using System.IdentityModel.Tokens.Jwt;
+using System.Security.Claims;
+using Domain.Exceptions;
+using Features.Auth.Identity;
+using Infrastructure.Configuration;
+using Infrastructure.Jwt;
+using Microsoft.AspNetCore.Identity;
+using Microsoft.Extensions.Configuration;
+
+namespace Features.Auth.Services;
+
+/// <summary>
+///     Default implementation of <see cref="ITokenService" /> that generates and validates JWTs
+///     for access, refresh, and confirmation flows using secrets read from configuration.
+/// </summary>
+public class TokenService : ITokenService
+{
+    private readonly string _accessTokenSecret;
+    private readonly string _confirmationTokenSecret;
+    private readonly string _refreshTokenSecret;
+    private readonly ITokenInfrastructure _tokenInfrastructure;
+    private readonly UserManager<ApplicationUser> _userManager;
+
+    /// <exception cref="InvalidOperationException">
+    ///     Thrown when any of the <c>ACCESS_TOKEN_SECRET</c>, <c>REFRESH_TOKEN_SECRET</c>, or
+    ///     <c>CONFIRMATION_TOKEN_SECRET</c> configuration values are not set.
+    /// </exception>
+    public TokenService(
+        ITokenInfrastructure tokenInfrastructure,
+        UserManager<ApplicationUser> userManager,
+        IConfiguration configuration
+    )
+    {
+        _tokenInfrastructure = tokenInfrastructure;
+        _userManager = userManager;
+
+        _accessTokenSecret = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.AccessTokenSecret
+        );
+
+        _refreshTokenSecret = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.RefreshTokenSecret
+        );
+
+        _confirmationTokenSecret = ConfigurationHelpers.GetKeyOrThrow(
+            configuration,
+            ConfigurationKeys.ConfirmationTokenSecret
+        );
+    }
+
+    /// <inheritdoc />
+    public string GenerateAccessToken(Guid userId, string username)
+    {
+        DateTime expiresAt = DateTime.UtcNow.AddHours(TokenServiceExpirationHours.AccessTokenHours);
+        return _tokenInfrastructure.GenerateJwt(userId, username, expiresAt, _accessTokenSecret);
+    }
+
+    /// <inheritdoc />
+    public string GenerateRefreshToken(Guid userId, string username)
+    {
+        DateTime expiresAt = DateTime.UtcNow.AddHours(
+            TokenServiceExpirationHours.RefreshTokenHours
+        );
+        return _tokenInfrastructure.GenerateJwt(userId, username, expiresAt, _refreshTokenSecret);
+    }
+
+    /// <inheritdoc />
+    public string GenerateConfirmationToken(Guid userId, string username)
+    {
+        DateTime expiresAt = DateTime.UtcNow.AddHours(
+            TokenServiceExpirationHours.ConfirmationTokenHours
+        );
+        return _tokenInfrastructure.GenerateJwt(
+            userId,
+            username,
+            expiresAt,
+            _confirmationTokenSecret
+        );
+    }
+
+    /// <inheritdoc />
+    public async Task<ValidatedToken> ValidateRefreshTokenAsync(string token)
+    {
+        return await ValidateTokenInternalAsync(token, _refreshTokenSecret, "refresh");
+    }
+
+    /// <inheritdoc />
+    public async Task<ValidatedToken> ValidateConfirmationTokenAsync(string token)
+    {
+        return await ValidateTokenInternalAsync(token, _confirmationTokenSecret, "confirmation");
+    }
+
+    /// <inheritdoc />
+    public async Task<RefreshTokenResult> RefreshTokenAsync(string refreshTokenString)
+    {
+        ValidatedToken validated = await ValidateRefreshTokenAsync(refreshTokenString);
+        ApplicationUser? user = await _userManager.FindByIdAsync(validated.UserId.ToString());
+        if (user == null)
+            throw new UnauthorizedException("User account not found");
+
+        string newAccess = GenerateAccessToken(user.Id, user.UserName);
+        string newRefresh = GenerateRefreshToken(user.Id, user.UserName);
+
+        return new RefreshTokenResult(user.Id, user.UserName, newRefresh, newAccess);
+    }
+
+    /// <summary>
+    ///     Performs the shared validation logic for access, refresh, and confirmation tokens:
+    ///     validates the JWT signature/expiration, then extracts and parses the user ID and username claims.
+    /// </summary>
+    /// <param name="tokenType">A human-readable label (e.g. "access", "refresh", "confirmation") used in error messages.</param>
+    /// <exception cref="UnauthorizedException">
+    ///     Thrown when required claims are missing, the user ID claim is not a valid <see cref="Guid" />,
+    ///     or the underlying token validation fails for any other reason (e.g. expired or invalid signature).
+    /// </exception>
+    private async Task<ValidatedToken> ValidateTokenInternalAsync(
+        string token,
+        string secret,
+        string tokenType
+    )
+    {
+        try
+        {
+            ClaimsPrincipal principal = await _tokenInfrastructure.ValidateJwtAsync(token, secret);
+
+            string? userIdClaim = principal.FindFirst(JwtRegisteredClaimNames.Sub)?.Value;
+            string? usernameClaim = principal.FindFirst(JwtRegisteredClaimNames.UniqueName)?.Value;
+
+            if (string.IsNullOrEmpty(userIdClaim) || string.IsNullOrEmpty(usernameClaim))
+                throw new UnauthorizedException(
+                    $"Invalid {tokenType} token: missing required claims"
+                );
+
+            if (!Guid.TryParse(userIdClaim, out Guid userId))
+                throw new UnauthorizedException($"Invalid {tokenType} token: malformed user ID");
+
+            return new ValidatedToken(userId, usernameClaim, principal);
+        }
+        catch (UnauthorizedException)
+        {
+            throw;
+        }
+        catch (Exception e)
+        {
+            throw new UnauthorizedException($"Failed to validate {tokenType} token: {e.Message}");
+        }
+    }
+}