RFC 8693 Token Exchange for Downstream API Access
Authorize the user via Auth Code + PKCE flow. The user's access token will be used as the subject token for the on-behalf-of exchange.
/oauth2/default/v1/authorize
Exchange the user's access token for a new token scoped to a downstream API. The service app acts on behalf of the user.
/oauth2/default/v1/token
grant_type=urn:ietf:params:oauth:grant-type:token-exchange
Test the exchanged access token by making an authenticated API request to a resource server.