Extract shared auth request validation

Endpoints/AuthValidator.cs

@@ -0,0 +1,77 @@
+using GameList.Contracts;
+
+namespace GameList.Endpoints;
+
+internal static class AuthValidator
+{
+    public const int MaxUsernameLength = 24;
+    public const int MaxDisplayNameLength = 16;
+    public const int MaxAdminKeyLength = 128;
+
+    public static bool TryValidateRegistration(RegisterRequest request, out ValidatedRegistration validated, out string error)
+    {
+        var username = (request.Username ?? string.Empty).Trim();
+        if (string.IsNullOrWhiteSpace(username) || username.Length > MaxUsernameLength)
+        {
+            validated = default;
+            error = $"Username is required and must be <= {MaxUsernameLength} characters.";
+            return false;
+        }
+
+        if (string.IsNullOrWhiteSpace(request.Password))
+        {
+            validated = default;
+            error = "Password is required.";
+            return false;
+        }
+
+        if ((request.DisplayName ?? string.Empty).Trim().Length > MaxDisplayNameLength)
+        {
+            validated = default;
+            error = $"Display name must be <= {MaxDisplayNameLength} characters.";
+            return false;
+        }
+
+        var displayName = EndpointHelpers.TrimTo(request.DisplayName, MaxDisplayNameLength);
+        if (string.IsNullOrWhiteSpace(displayName))
+        {
+            validated = default;
+            error = "Display name is required.";
+            return false;
+        }
+
+        var adminKey = EndpointHelpers.TrimTo(request.AdminKey, MaxAdminKeyLength);
+        validated = new ValidatedRegistration(username, username.ToLowerInvariant(), displayName, adminKey);
+        error = string.Empty;
+        return true;
+    }
+
+    public static bool TryValidateLogin(LoginRequest request, out string username, out string normalizedUsername, out string error)
+    {
+        username = (request.Username ?? string.Empty).Trim();
+        normalizedUsername = string.Empty;
+
+        if (string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(request.Password))
+        {
+            error = "Username and password are required.";
+            return false;
+        }
+
+        if (username.Length > MaxUsernameLength)
+        {
+            error = $"Username must be <= {MaxUsernameLength} characters.";
+            return false;
+        }
+
+        normalizedUsername = username.ToLowerInvariant();
+        error = string.Empty;
+        return true;
+    }
+
+    public readonly record struct ValidatedRegistration(
+        string Username,
+        string NormalizedUsername,
+        string DisplayName,
+        string? AdminKey
+    );
+}