Background: For dynamic clients, the groups scope is not always allowed
and/or requested by the client, so it will not always be granted by the
Supervisor for an authorization request.
Previously, when the groups scope was not granted, we would skip
searching for upstream groups in some scenarios.
This commit changes the behavior of authorization flows so that even
when the groups scope is not granted we still search for the upstream
group memberships as configured, and we pass the upstream group
memberships into any configured identity transformations. The identity
transformations could potentially reject the user's authentication based
on their upstream group membership.
When the groups scope is not granted, we don't include the groups in
the final Supervisor-issued ID token. This behavior is not changed.
Each endpoint handler is now responsible for applying the identity
transformations and creating most of the session data, rather than each
implementation of the upstream IDP interface. This shares code better,
and reduces the responsibilities of the implementations of the IDP
interface by letting them focus more on the upstream stuff.
Also refactor the parameters and return types of the IDP interfaces to
make them more clear, and because they can be more focused on upstream
identities (pre-identity transformation). This clarifies the
responsibilities of the implementations of the IDP interface.
Create an interface to abstract the upstream IDP from the
authorize, IDP discovery, callback, choose IDP, and login
endpoints. This commit does not refactor the token endpoint,
which will be refactored in a similar way in the next commit.
