On RHEL 7 (OpenSSL 1.0.x), EVP_DigestVerifyFinal expects its second argument to be of type unsigned char*. On RHEL 8 (OpenSSL 1.1.x), EVPDigestVerifyFinal expects its second argument to be of type const unsigned char*. Today, we are casting the signature to const unsigned char* before passing it to the function here, triggering a compiler error on platforms with older versions of OpenSSL. 

We should update the cast so it succeeds on older versions of OpenSSL as well.