suggestion for better error handling

[tomk3003]

In case of problems during the OIDC warmup, there is only an error message being logged but the plugin still proceeds with every following authentication attempt resulting in an error.
I do not see any way to handle the warmup error with e.g. an error handler or to make the error fatal.

One of those would be nice to have.
At the moment the only way is to check for valid provider URLs after plugin registration.

[jhthorsen]

I can't remember the reasoning behind that... I think I welcome a PR to change the default, but it would be even easier to merge a change that takes a config parameter 👍

[tomk3003]

I am busy for the next 2 weeks and will provide a PR after that.
I agree that a config parameter would be best.

[tomk3003]

@jhthorsen: did you have time to look at PR #78 yet?