Feature request: Support Client ID Metadata Documents

[FenTiger]

IndiePass currently provides a URL to a HTML page as its client_id parameter.

The latest IndieAuth spec recommends making this URL point to a JSON file instead.

See: https://github.com/indieweb/indieauth/issues/133 and https://indieauth.spec.indieweb.org/#client-information-discovery

Hopefully this should be as simple as providing a suitable JSON file on https://indiepass.app/ and changing the client ID to point to it.