We are developing an application in a microservice architecture, which implements signle sign-on using Spring Cloud OAuth2 on multiple OAuth2 providers like Google and Facebook. We are also developing our own authorization server, and will be integrated on next release.
Now, on our microservices, which are resource servers, I would like to know how to handle multiple token-info-uri or user-info-uri to multiple authorization servers (e.g. for Facebook or Google).
This type of situation is generally solved by having a middle-man; a single entity that your resource servers trust and that can be used to normalize any possible differences that surface from the fact that users may authenticate with distinct providers. This is sometimes referred to as a federation provider.
Auth0 is a good example on this kind of implementation. Disclosure: I'm an Auth0 engineer.
Auth0 sits between your app and the identity provider that authenticates your users. Through this level of abstraction, Auth0 keeps your app isolated from any changes to and idiosyncrasies of each provider's implementation.
(emphasis is mine)
It's not that your resource servers can't technically trust more than one authorization server, it's just that moving that logic out of the individual resource servers into a central location will make it more manageable and decoupled.
Also have in mind that authentication and authorization are different things although we are used to seeing them together. If you're going to implement your own authorization server, you should make that the central point that can:
