Show a user's avatar on the public profile (#333)

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

@@ -1,19 +1,39 @@
 using Domain.Entities;
+using Features.ImageUploads.Services;
 
 namespace Features.Users.Dtos;
 
 /// <summary>Converts user domain entities into API response models.</summary>
 public static class UserDtoMapper
 {
+    /// <summary>
+    ///     How long a presigned avatar URL stays valid. Long enough to outlive the page that embeds it,
+    ///     short enough that a leaked URL stops working.
+    /// </summary>
+    public static readonly TimeSpan AvatarUrlLifetime = TimeSpan.FromHours(1);
+
     /// <summary>Converts a user account into its public-profile representation.</summary>
-    public static PublicUserProfileDto ToPublicProfileDto(this UserAccount user)
+    /// <param name="user">The account to convert.</param>
+    /// <param name="fileStorageProvider">
+    ///     Signs the download URL for the account's avatar. <c>Photo.Hyperlink</c> holds an object key
+    ///     rather than a URL, so it has to be signed before a client can fetch it.
+    /// </param>
+    public static PublicUserProfileDto ToPublicProfileDto(
+        this UserAccount user,
+        IFileStorageProvider fileStorageProvider
+    )
     {
+        string? avatarKey = user.UserAvatar?.Photo?.Hyperlink;
+
         return new PublicUserProfileDto(
             UserAccountId : user.UserAccountId,
             Username : user.Username,
             FirstName : user.FirstName,
             LastName : user.LastName,
             Biography : user.UserProfile?.Biography ?? string.Empty,
+            AvatarUrl : string.IsNullOrWhiteSpace(avatarKey)
+                ? string.Empty
+                : fileStorageProvider.GetPresignedUrl(avatarKey, AvatarUrlLifetime),
             CreatedAt : user.CreatedAt
         );
     }

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

@@ -7,5 +7,6 @@ public record PublicUserProfileDto(
     string FirstName,
     string LastName,
     string Biography,
+    string AvatarUrl,
     DateTime CreatedAt
 );