OIDC flow

[daurnimator]

For login to various hashbang apps/services it would be useful to use the userdb as a backend for an OIDC flow.
Needs research into options.

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Notes:

• https://connect2id.com/learn/openid-connect
• Need to implement /.well-known/openid-configuration with at least issuer and authorization_endpoint fields.
• Need to implement the authorization_endpoint, query params are:
  • claims
  • client_id
  • nonce
  • redirect_uri
  • response_type
  • scope
  • state