OIDC Timeout and Web UI

[russjones]

Issue

At the moment when you start the OIDC login process you have 60 seconds to complete it:

https://github.com/gravitational/teleport/blob/master/lib/auth/auth.go#L756-L759
https://github.com/gravitational/teleport/blob/master/lib/defaults/defaults.go#L114-L115

If you are not able able authenticate within 60 seconds (as in the callback is not received within 60 seconds), the request (and state token contained within) that is stored on the backend is deleted.

When the callback does arrive, it can no longer find the request (and the state token needed to verify the request is valid), the following is presented to the user in the browser:

{"message":"[web connectors oidc requests]: c94b359a1b1c11e793b7ac87a30d221b not found"}

Proposed Fix

• We improve the UX for timeout messages. While the JSON message is accurate, it's not helpful in resolving the issue.
• We make the timeout configurable in the OIDC connector.