docs: def register_pubkey(self):
          """
          XXX Check that the pubkey received is in the group.
          """
          p = pkcs_os2ip(self.dh_p)
          g = pkcs_os2ip(self.dh_g)
          pn = dh.DHParameterNumbers(p, g)
  
          y = pkcs_os2ip(self.dh_Ys)
          public_numbers = dh.DHPublicNumbers(y, pn)
  
          s = self.tls_session
          s.server_kx_pubkey = public_numbers.public_key(default_backend())
  
          if not s.client_kx_ffdh_params:
              s.client_kx_ffdh_params = pn.parameters(default_backend())