N+ OIDC Reference Implementation w/ Auth0 Audience Claim for Partner API

[shawnhankim]

Background:

• Currently, NGINX Plus OIDC Reference Implementation doesn't use aud claim in the request of IdP authorization endpoint. - Auth0 returns empty payload in the access token from the token endpoint.
• NGINX Developer Portal needs the access token that contains custom claims to handle partner APIs.

AC:

• Investigate and document how to add custom claims that contains groups and sub-groups.
• Reference implementation to handle aud claims in the request of IdP authorization endpoint.
• Guideline: OIDC Policy for the customizable parameters for the IdP authorization endpoint.
• ACM converter update if necessary based on the change of reference implementation.