title: OpenIdConnect signin-oidc route not handled by ASP.NET MVC
body: <p>I am using an external OIDC identity provider to log my users into my webshop. The webshop is being built on ASP.NET MVC with .NET Framework 4.7.2.</p>
  
  <p>I have started using the basic MVC template and adding my authentication code. </p>
  
  <pre><code>public void ConfigureAuth(IAppBuilder app)
  {
  
      JwtSecurityTokenHandler.DefaultInboundClaimTypeMap.Clear();// = new Dictionary&lt;string, string&gt;();
  
      app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType);
  
      app.UseCookieAuthentication(new CookieAuthenticationOptions
      {
          AuthenticationType = CookieAuthenticationDefaults.AuthenticationType
      });
  
      var authority = "https://authentication.myOpenIdProvider.com/auth/oauth2/realms/root/realms/test";
      var redirectUri = "http://localhost:8888/signin-oidc";
      var postlogoUri = "http://localhost:8888/signout-callback-oidc";
      var clientId = "MyClientId";
      var clientSecret = "MyClientSecret";
  
      app.UseOpenIdConnectAuthentication(new OpenIdConnectAuthenticationOptions
      {
          ClientId = clientId,
          ClientSecret = clientSecret,
          Authority = authority,
          RedirectUri = redirectUri,
          PostLogoutRedirectUri = postlogoUri,
          ResponseType = "code",
          Scope = "openid favorites",
          SignInAsAuthenticationType = "Cookies",
          RequireHttpsMetadata = false,
      });
  }
  </code></pre>
  
  <p>When i hit login on my page, i get redirected to my authentication provider, also the correct redirectUri is passed. </p>
  
  <pre><code>public class AccountController : Controller
  {
      public ActionResult Login()
      {
          if (!HttpContext.User.Identity.IsAuthenticated)
          {
              HttpContext.GetOwinContext().Authentication.Challenge(OpenIdConnectAuthenticationDefaults.AuthenticationType);
              return new HttpUnauthorizedResult();
          }
  
          return RedirectToAction("Index", "Home");
      }
  
      ... 
  }
  </code></pre>
  
  <p>However, after i succesfully authenticate with my external provider and get redirected to my site (currently its just <a href="http://localhost:8888/signin-oidc" rel="noreferrer">http://localhost:8888/signin-oidc</a> for dev purposes) the route is not handled. I am getting a 404, so something clearly isn't working like it is supposed to do.</p>
  
  <p>I have installed ELMAH and this reports the following exception message:</p>
  
  <blockquote>
    <p>System.Web.HttpException (0x80004005): The controller for path '/signin-oidc' was not found or does not implement IController.</p>
  </blockquote>
  
  <p>For context: The same works in an ASP.NET Core API, using the same external openid provider with identical configuration.</p>