offline Relying-Party registrations

[peppelinux]

Each new registration of an RP with an OP requires that the OP make N connections with third-party systems.

This can unfortunately produce a timeout of the connection on the user-agent side during the authorization request phase.

Furthermore, on behalf of a single RP, never seen before by an OP, several user-agents can request authentication from the same OP to the same parties. This produces a concurrent number of equivalent requests to the OP to terminate the trust chain.

I believe this issue can be optionally mitigated by allowing all OP to periodically update their definitions through an effective use of the Entity Listing endpoint, whose improvement proposal (hopefully) is here:

#67