these controls set what the algorithm should be, and the engine that
implements the algorithm if needed.
+Note that not all algorithms may support all digests. HMAC does not support
+variable output length digests such as SHAKE128 or SHAKE256.
+
B<EVP_MAC_CTRL_SET_ENGINE> takes one argument: C<ENGINE *>
B<EVP_MAC_CTRL_SET_MD> takes one argument: C<EVP_MD *>