add the option of a custom JWT issuer

at the moment (2.9) there are 2 options in terms OIDC Authentication: RHSSO and OIDC compliant IDP with no dynamic client registration feature.

Some customers have in house built IDP based for example on SpringBoot (which has a quite popular JWT set of libraries). This is especially true for internal microservices scenarios.

In these cases it would be nice t have a third option in terms of OIDC authentication where the customer can manually:

• define the auth endpoint of the customer issuer
• define the token endpoint of the customer issuer
• define the value of the issuer
• upload the public key to verify signature