OSSL_PKEY_PARAM_RSA_MGF1_DIGEST
const char *key_mgf1_md = OSSL_PKEY_PARAM_RSA_MGF1_DIGEST;
param_mgf1md = OSSL_PARAM_locate_const(params, OSSL_PKEY_PARAM_RSA_MGF1_DIGEST);
OSSL_PARAM_utf8_string(OSSL_PKEY_PARAM_RSA_MGF1_DIGEST, NULL, 0), \