Discover OIDC server config at runtime

With us wanting to support multiple OIDC implementations we need to discover the endpoints etc for the specific implementation.

We could use https://openid.net/specs/openid-connect-discovery-1_0.html and fetch the data at runtime and cache it for an hour.

For example in our case with Keycloak this is: https://auth-demo.tugraz.at/auth/realms/tugraz-vpu/.well-known/openid-configuration

I hope other OIDC implementations support this spec, and if not we can point to the spec at least... or support a way to read the spec data locally.