@Override
        protected void updateDirect(long ptr, int len) {
            final NativeRef.HMAC_CTX ctxLocal = ctx;
            NativeCrypto.HMAC_UpdateDirect(ctxLocal, ptr, len);
        }
Holds the EVP_MD for the hashing algorithm, e.g.
EVP_get_digestbyname("sha1");
common/src/main/java/org/conscrypt/OpenSSLMac.java