Credentials

  (input/optional)
          A pointer to a CSSM_TUPLEGROUP containing a group of
          certificates, in TUPLE form. The tuple-certificates define
          the delegation of authorizations from the BaseAuthorizations
          to the Requestors.  If no additional authorization-granting
          tuples are provided, then this value is NULL and the
          BaseAuthorizations are the only source of trusted
          authorizations used as input to the authorization computation.