I have this ASP.NET MVC application using a Discord OAuth2 login to take username and ID. The problem is, no matter what I do, despite the URI PathString /signin-discord correctly directed to a method that returns a .cshtml view, it is instead always resulting in an “HTTP Error 500”.

I honestly have no idea what I did wrong that the URI isn’t properly returning the view.

Here is my configuration for Discord OAuth2 authentication:

[HttpGet("/signin-discord")]
public async Task<IActionResult> ExternalLoginCallback()
{
   var authenticateResult = await HttpContext.AuthenticateAsync("Discord");

   if (!authenticateResult.Succeeded)
   {
       // Handle authentication failure
       return RedirectToAction("Login", "Account"); // Redirect to login page or handle as needed
   }

   // Retrieve Discord user information
   var userId = authenticateResult.Principal.FindFirst(ClaimTypes.NameIdentifier)?.Value;
   var username = authenticateResult.Principal.FindFirst(ClaimTypes.Name)?.Value;

   // Example: Authenticate user locally (store in session or database)
   var claims = new[]
   {
       new Claim(ClaimTypes.NameIdentifier, userId),
       new Claim(ClaimTypes.Name, username),
       // Add additional claims as needed
   };

   var identity = new ClaimsIdentity(claims, "Discord");
   var principal = new ClaimsPrincipal(identity);

   // Sign in the user
   await HttpContext.SignInAsync(CookieAuthenticationDefaults.AuthenticationScheme, principal);

   // Redirect to your viewer page or any desired endpoint
   return View("DrawingPad"); // This will render Views/Drawing/DrawingPad.cshtml

   //return RedirectToAction("DrawingPad", "Drawing");
}

I tried adjusting the Controller Method meant to be invoked by the URI, and setting its signature right at /signin-discord.

[HttpGet("/signin-discord")]
public async Task<IActionResult> ExternalLoginCallback()
//return RedirectToAction("Index", "Home");}

But nothing worked.