Keycloak OpenID flow

On top of authz code grant flow, allows an iOs cleint app to login as a keycloak user.

Have a xib button (customizable?) that link to auth endpoint. Main difference on keycloak configuration is the need to add claim in order to be able to retrieve user information.

Those information are encoded in the token itseft. Decoding is needed.
See:
https://github.com/keycloak/keycloak/blob/7f4849e16590bc4268a7fcb454cc3b9a7814d93f/core/src/main/java/org/keycloak/jose/jws/JWSInput.java

https://github.com/keycloak/keycloak/blob/7f4849e16590bc4268a7fcb454cc3b9a7814d93f/core/src/main/java/org/keycloak/util/Base64Url.java