The content type header contains full mimetype string which might
contain parameters. The getJSON function doesn't account for this and so
some responses fail to parse although they are perfectly acceptable. For
example
```
curl -vv 'https://github.com/.well-known/oauth-authorization-server/login/oauth'
```
returns a content type header with the value
```
content-type: application/json; charset=utf-8
```
which is perfectly valid but fails in the current logic.
Use URL scheme validation for remaining URL fields in auth
datastructures (AuthServerMeta and ClientRegistrationMetadata), to
prevent XSS attacks.
By comparison, the typescript SDK doesn't validate
introspection_endpoint, and I don't know why. Otherwise the
implementations align.
Fixes#526
GetProtectedResourceMetadataFromHeader was validating the resource field
against the metadata endpoint URL instead of the original server URL.
Per RFC 9728 section 3.3, the resource field must match the URL that the
client used to make the request to the resource server.
Fixes: #560
This package will hold externally visible parts of internal/oauthex.
For now, just add an alias to the ProtectedResourceMetadata struct. This
lets one write MCP-compliant servers.
