The $ACM service provides a common interface to all functions
    supported by the Authentication and Credential Management (ACM)
    authority.

    The caller must specify the function code and any applicable
    function modifiers and item codes for the requested operation.

    The $ACM service completes asynchronously; for synchronous
    completion, use the $ACMW form of the service.

    Format

      SYS$ACM  [efn], func, [context], itmlst, acmsb, [astadr],

               [astprm]

    C Prototype

      int sys$acm  (unsigned int efn, unsigned int func, struct

                   _acmecb **context, void *itmlst, struct _acmesb

                   *acmsb, void (*astadr)(__unknown_params), int

                   astprm);