Return the TLSCiphertext.encrypted_record for AEAD ciphers.

def _tls_auth_encrypt(self, s):
        """
        Return the TLSCiphertext.encrypted_record for AEAD ciphers.
        """
        wcs = self.tls_session.wcs
        write_seq_num = struct.pack("!Q", wcs.seq_num)
        wcs.seq_num += 1
        return wcs.cipher.auth_encrypt(s, b"", write_seq_num)