Add support for Subject Identifier Type: pairwise

[Revsgaard]

Add support for pairwise SUB and add information in OpenID Connect Discovery.

https://openid.net/specs/openid-connect-core-1_0.html#SubjectIDTypes

To protect the End-User from possible correlation among Clients, the use of a Pairwise Pseudonymous Identifier (PPID) as the sub (subject) SHOULD be considered.