Create proper login page/actually log out when using Okta

[mbland]

Right now, when accessing the server, you're instantly redirected to the auth provider's login page. If the login fails, you're immediately redirected back to that page.

Most of the time this isn't an issue, but if the user is legitimately logged in and there's a problem with the auth flow on our side, this manifests as a "too many redirects" error.

It'd be better to log the error in the /auth/callback endpoint, and present a proper /login endpoint or some such.

cc: @akashvbabu