Description of problem:
When configured with a single identity provider that's not capable of login authentication flows, the oauth-server returns error when accessed from the browser. When the oauth-server is accessed from the web console, this error causes redirect loop between the oauth-server and the console.

Version-Release number of selected component (if applicable):
4.5

How reproducible:
100%

Steps to Reproduce:
1. configure request header IdP with some bogus ChallengeURL and no LoginURL
2. disable the kubeadmin user by deleting the kube-system/kubeadmin secret
3. wait for the changes to be applied to the oauth-server's deployment
4. go to the console's URL

Actual results:
The console tries to access a resource, gets "unauthorized" error, redirects user to the oauth-server, the oauth-server errors out because it does not allow browser login, redirects user to console, and the loop repeats infinitely.

Expected results:
The oauth-server presents the user with a login page that won't allow them to log in OR the server errors out with a clear error that tells the console not to try to loop back to it again.