OpenSSL::X509::Request#sign

static VALUE
ossl_x509req_sign(VALUE self, VALUE key, VALUE digest)
{
    X509_REQ *req;
    EVP_PKEY *pkey;
    const EVP_MD *md;

    GetX509Req(self, req);
    pkey = GetPrivPKeyPtr(key); /* NO NEED TO DUP */
    if (NIL_P(digest)) {
        md = NULL; /* needed for some key types, e.g. Ed25519 */
    } else {
        md = ossl_evp_get_digestbyname(digest);
    }
    if (!X509_REQ_sign(req, pkey, md)) {
        ossl_raise(eX509ReqError, NULL);
    }

    return self;
}