Is generally aligned with out SAML2 group sync functionality, but for
OIDC based upon feedback in #3004.
Neeeded the tangental addition of being able to define custom scopes on
the initial auth request as some systems use this to provide additional
id token claims such as groups.
Includes tests to cover.
Tested live using Okta.
Fixes issue where certain errors would not show to the user
due to extra navigation jumps which lost the error message
in the process.
This simplifies and aligns exceptions with more directly
handled exception usage at the controller level.
Fixes#3264
