Fix test endpoints and username length handling in OAuth service

- Fix profile update endpoint URL in tests (/api/Account/Update instead of /api/Account/Profile)
- Add username length validation in OAuth service (max 16 chars with conflict resolution)
- Register OAuth services in Program.cs via ConfigureOAuth()
- Add debug output to OAuth integration tests

Remaining issues to fix:
- OAuth endpoints returning HTML instead of JSON in tests (route matching issue)
- Test database not being cleaned between tests
- OAuth login not properly checking disabled providers
- Username conflict test expectations need adjustment after truncation fix

Co-authored-by: GZTimeWalker <28180262+GZTimeWalker@users.noreply.github.com>

Author: Copilot

src/GZCTF.Integration.Test/Tests/Api/OAuthIntegrationTests.cs

@@ -104,6 +104,12 @@ public async Task User_GetOAuthProviders_ReturnsEnabledProviders()
         using var publicClient = factory.CreateClient();
         var response = await publicClient.GetAsync("/api/Account/OAuth/Providers");
 
+        // Debug output
+        output.WriteLine($"Response status: {response.StatusCode}");
+        output.WriteLine($"Response content type: {response.Content.Headers.ContentType}");
+        var content = await response.Content.ReadAsStringAsync();
+        output.WriteLine($"Response content (first 500 chars): {content[..Math.Min(500, content.Length)]}");
+
         // Assert
         response.EnsureSuccessStatusCode();
         var availableProviders = await response.Content.ReadFromJsonAsync<Dictionary<string, string>>();

src/GZCTF.Integration.Test/Tests/Api/UserMetadataTests.cs

@@ -252,7 +252,7 @@ public async Task User_UpdateProfile_WithMetadata_Succeeds()
             }
         };
 
-        var response = await userClient.PutAsJsonAsync("/api/Account/Profile", updateModel);
+        var response = await userClient.PutAsJsonAsync("/api/Account/Update", updateModel);
         output.WriteLine($"Status: {response.StatusCode}");
 
         // Assert
@@ -285,7 +285,7 @@ public async Task User_UpdateProfile_RemoveMetadata_Succeeds()
                 { "testField", "testValue" }
             }
         };
-        await client.PutAsJsonAsync("/api/Account/Profile", addModel);
+        await client.PutAsJsonAsync("/api/Account/Update", addModel);
 
         // Act - remove metadata by setting to empty string
         var removeModel = new ProfileUpdateModel
@@ -295,7 +295,7 @@ public async Task User_UpdateProfile_RemoveMetadata_Succeeds()
                 { "testField", "" }
             }
         };
-        var response = await client.PutAsJsonAsync("/api/Account/Profile", removeModel);
+        var response = await client.PutAsJsonAsync("/api/Account/Update", removeModel);
 
         // Assert
         response.EnsureSuccessStatusCode();

src/GZCTF/Program.cs

@@ -38,6 +38,7 @@
 builder.ConfigureStorage();
 builder.ConfigureCacheAndSignalR();
 builder.ConfigureIdentity();
+builder.ConfigureOAuth();
 builder.ConfigureTelemetry();
 
 builder.AddServiceConfigurations();

src/GZCTF/Services/OAuth/OAuthService.cs

@@ -154,12 +154,23 @@ public class OAuthService(
         // Create new user
         var userName = oauthUser.UserName ?? oauthUser.Email.Split('@')[0];
 
+        // Truncate username if too long (max 16 characters, leave room for counter)
+        const int maxUsernameLength = 16;
+        if (userName.Length > maxUsernameLength - 3) // Reserve 3 chars for potential counter (e.g., "123")
+        {
+            userName = userName[..(maxUsernameLength - 3)];
+        }
+        
         // Ensure username is unique
         var baseUserName = userName;
         var counter = 1;
         while (await userManager.FindByNameAsync(userName) is not null)
         {
-            userName = $"{baseUserName}{counter}";
+            var suffix = counter.ToString();
+            var maxBaseLength = maxUsernameLength - suffix.Length;
+            userName = baseUserName.Length > maxBaseLength 
+                ? $"{baseUserName[..maxBaseLength]}{suffix}"
+                : $"{baseUserName}{suffix}";
             counter++;
         }