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.

[matthieusieben]

Could the error you got be something like the following?

Invalid client configuration: [
  {
    "code": "invalid_type",
    "expected": "object",
    "received": "array",
    "path": [
      "jwks"
    ],
    "message": "Expected object, received array"
  }
]

The jwks property must be an object with a keys property that is an array.

{
  "client_id": "https://foo.bar/baz.json",
  "jwks": {
    "keys": [
      { ... }
    ]
  }
}