docs: def _tls_auth_encrypt(self, s):
          """
          Return the TLSCiphertext.fragment for AEAD ciphers, i.e. the whole
          GenericAEADCipher. Also, the additional data is computed right here.
          """
          write_seq_num = struct.pack("!Q", self.tls_session.wcs.seq_num)
          self.tls_session.wcs.seq_num += 1
          add_data = (write_seq_num +
                      pkcs_i2osp(self.type, 1) +
                      pkcs_i2osp(self.version, 2) +
                      pkcs_i2osp(len(s), 2))
          return self.tls_session.wcs.cipher.auth_encrypt(s, add_data,
                                                          write_seq_num)