Allow additional provider-specific fields
OAuth 2.0 authorization endpoint
Optionalcode_Optional: Supported PKCE code challenge methods (RFC 7636)
Optionalgrant_Optional: Supported grant types
Authorization server issuer URL
Dynamic Client Registration endpoint (RFC 7591)
Optionalresponse_Optional: Supported response types
Optionalrevocation_Optional: Token revocation endpoint
Optionalscopes_Optional: Supported OAuth scopes
Optionalservice_Optional: Service documentation URL
OAuth 2.0 token endpoint
Optionaltoken_Optional: Supported token endpoint auth methods
RFC 8414 Authorization Server Metadata
See
https://www.rfc-editor.org/rfc/rfc8414.html