X509_to_X509_REQ
if ((rreq = X509_to_X509_REQ(req, NULL, EVP_md5())) == NULL)
rq = X509_to_X509_REQ(x, pk, x509_config.digest);
X509_REQ * X509_to_X509_REQ(X509 *x, EVP_PKEY *pkey, const EVP_MD *md);