OAuth provider: fix in-line JWKs support in client-metadata.json

[bnewbold]

We support both jwks and jwks_uri in client-metadata. When I was experimenting, the jwks ("inline" keys in the client-metadata document itself) didn't work though. I can see there is code for it, but I don't think any tests.

It is conceivable that I had an error in my client code, but I did double-check and things worked immediately with jwks_uri.