Support OpenID Connect Discovery

[alexandroid]

From README it looks like appAuthHelper configuration takes all the endpoints directly.

Please consider supporting OpenID Connect Discovery spec i.e. automatically reading the endpoints and other parameters from /.well-known/openid-configuration. It will further simplify the interface and help to "future proof" against the configuration changes on the OpenID provider side.

[jakefeasel]

I've considered that option and while I agree it's better for future-proofing, it does mean that every single time the SPA loads, it has to do one more HTTP request (to the well-known endpoint). I suppose we could consider caching it in the browser, so at least it doesn't load every time for every user, but even still it means we would be calling it a lot (at least once per user). Caching the well-known endpoint also is somewhat counter-productive in terms of "future proofing", since we then have to deal with cache management (when to expire the cache? etc...).

I suppose as the appAuthHelper developer I could just leave this as a choice / problem for the individual user to grapple with - either use the explicit endpoints or call the well-known one. I just personally wouldn't use the well-known endpoint for the reasons above, so I'm curious whether or not others would feel the same.