client_id and client_secret (using grant_type: client_credentials) to B's token endpoint. B validates these credentials and, if successful, returns a Bearer access_token, token_type, and expires_in. This access token must be included in the Authorization header (e.g., Authorization: Bearer ) for all subsequent API calls to B's protected resources.x-www-form-urlencoded body type.access_token (string): The access token for the identity verification.token_type (string): The type of token.expires_in (integer): The duration for which the token is valid.scope (string): The scope of the token.