diff --git a/web/backend/Features/Features.Auth/Services/TokenService.cs b/web/backend/Features/Features.Auth/Services/TokenService.cs
index e766c415..8ed118a2 100644
--- a/web/backend/Features/Features.Auth/Services/TokenService.cs
+++ b/web/backend/Features/Features.Auth/Services/TokenService.cs
@@ -106,16 +106,16 @@ public class TokenService : ITokenService
         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(
+    /// <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
diff --git a/web/backend/Infrastructure/Infrastructure.PasswordHashing/Argon2Infrastructure.cs b/web/backend/Infrastructure/Infrastructure.PasswordHashing/Argon2Infrastructure.cs
index bda6f8ad..b938365e 100644
--- a/web/backend/Infrastructure/Infrastructure.PasswordHashing/Argon2Infrastructure.cs
+++ b/web/backend/Infrastructure/Infrastructure.PasswordHashing/Argon2Infrastructure.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Security.Cryptography;
 using System.Text;
 using Konscious.Security.Cryptography;
@@ -13,26 +14,32 @@ public class Argon2Infrastructure : IPasswordInfrastructure
     private const int HashSize = 32; // 256-bit
     private const int ArgonIterations = 4;
     private const int ArgonMemoryKb = 65536; // 64MB
+    private const int DegreeOfParallelism = 2; // Hardcoded to prevent thread pool exhaustion
 
-    /// <inheritdoc />
-    /// <returns>A string of the form <c>"{base64Salt}:{base64Hash}"</c>, suitable for storage.</returns>
     public string Hash(string password)
     {
         byte[] salt = RandomNumberGenerator.GetBytes(SaltSize);
-        Argon2id argon2 = new(Encoding.UTF8.GetBytes(password))
+
+        using Argon2id argon2 = new(Encoding.UTF8.GetBytes(password))
         {
             Salt = salt,
-            DegreeOfParallelism = Math.Max(Environment.ProcessorCount, 1),
+            DegreeOfParallelism = DegreeOfParallelism,
             MemorySize = ArgonMemoryKb,
             Iterations = ArgonIterations,
         };
 
         byte[] hash = argon2.GetBytes(HashSize);
-        return $"{Convert.ToBase64String(salt)}:{Convert.ToBase64String(hash)}";
+
+        // The PHC string standard requires Base64 without the trailing '=' padding characters
+        string b64Salt = Convert.ToBase64String(salt).TrimEnd('=');
+        string b64Hash = Convert.ToBase64String(hash).TrimEnd('=');
+
+        // Argon2 version is currently 19 (0x13 in hex)
+        return $"$argon2id$v=19$m={ArgonMemoryKb},t={ArgonIterations},p={DegreeOfParallelism}${b64Salt}${b64Hash}";
     }
 
     /// <inheritdoc />
-    /// <remarks>Uses a fixed-time comparison to mitigate timing attacks.</remarks>
+    /// <remarks>Uses a fixed-time comparison to mitigate timing attacks. Supports standard PHC string format.</remarks>
     /// <returns>
     ///     <c>false</c> if the password doesn't match, if <paramref name="stored" /> is malformed, or if any
     ///     other error occurs during verification.
@@ -41,27 +48,58 @@ public class Argon2Infrastructure : IPasswordInfrastructure
     {
         try
         {
-            string[] parts = stored.Split(':', StringSplitOptions.RemoveEmptyEntries);
-            if (parts.Length != 2)
+            // Split the PHC format: $argon2id$v=19$m=65536,t=3,p=4$salt$hash
+            string[] parts = stored.Split('$', StringSplitOptions.RemoveEmptyEntries);
+
+            // We expect exactly 5 parts when empty entries (the one before the first $) are removed
+            if (parts.Length != 5 || parts[0] != "argon2id")
                 return false;
 
-            byte[] salt = Convert.FromBase64String(parts[0]);
-            byte[] expected = Convert.FromBase64String(parts[1]);
+            int memory = 0,
+                iterations = 0,
+                parallelism = 0;
+            string[] parameters = parts[2].Split(',');
 
-            Argon2id argon2 = new(Encoding.UTF8.GetBytes(password))
+            foreach (string param in parameters)
+            {
+                if (param.StartsWith("m="))
+                    memory = int.Parse(param.Substring(2));
+                else if (param.StartsWith("t="))
+                    iterations = int.Parse(param.Substring(2));
+                else if (param.StartsWith("p="))
+                    parallelism = int.Parse(param.Substring(2));
+            }
+
+            byte[] salt = DecodeBase64NoPadding(parts[3]);
+            byte[] expectedHash = DecodeBase64NoPadding(parts[4]);
+
+            // Use the parameters embedded in the stored string, so previously hashed
+            // passwords remain verifiable after a parameter change.
+            using Argon2id argon2 = new(Encoding.UTF8.GetBytes(password))
             {
                 Salt = salt,
-                DegreeOfParallelism = Math.Max(Environment.ProcessorCount, 1),
-                MemorySize = ArgonMemoryKb,
-                Iterations = ArgonIterations,
+                DegreeOfParallelism = parallelism,
+                MemorySize = memory,
+                Iterations = iterations,
             };
 
-            byte[] actual = argon2.GetBytes(expected.Length);
-            return CryptographicOperations.FixedTimeEquals(actual, expected);
+            byte[] actualHash = argon2.GetBytes(expectedHash.Length);
+
+            return CryptographicOperations.FixedTimeEquals(actualHash, expectedHash);
         }
         catch
         {
             return false;
         }
     }
+
+    /// <summary>
+    /// .NET's Convert.FromBase64String requires padding. The PHC format drops padding.
+    /// This helper restores the padding before converting.
+    /// </summary>
+    private static byte[] DecodeBase64NoPadding(string base64)
+    {
+        string padded = base64.PadRight(base64.Length + (4 - base64.Length % 4) % 4, '=');
+        return Convert.FromBase64String(padded);
+    }
 }