public static byte[] getTlsUnique(SSLSocket socket) {
        return toConscrypt(socket).getTlsUnique();
    }
Returns the tls-unique channel binding value for this connection, per RFC 5929.  This
will return {@code null} if there is no such value available, such as if the handshake
has not yet completed or this connection is closed.
common/src/main/java/org/conscrypt/Conscrypt.java