DPoP: Extending Client to store Client ID (Linked-Data Resource)

In the Solid-OIDC Primer the client-id given is a linked-data resource

Currently, the Client model stores an id (internal) and a website (homepage), neither of which are suitable for this purpose

We should extend the model, or possibly replace the internal client id with the linked-data resource format

This is non-blocking as we can store it in the website field in the short-term

...

Also required from the Solid-OIDC Spec:

If an app WebID is provided as the client id (see note above to see other options), we must fetch that app WebID to confirm its validity.

This will require work RS-side as well (djangoldp_account)

• AuthorizeEndpoint.validate_params should also validate the redirect_uri matches the client ID