code: def verify_client(self, client_jid = None, domains = None):
          
          jids = [jid for jid in self.get_jids() if jid.local]
          if not jids:
              return None
          if client_jid is not None and client_jid in jids:
              return client_jid
          if domains is None:
              return jids[0]
          for jid in jids:
              for domain in domains:
                  if are_domains_equal(jid.domain, domain):
                      return jid
          return None
docs: Verify certificate for a client.
  
          Please note that `client_jid` is only a hint to choose from the names,
          other JID may be returned if `client_jid` is not included in the
          certificate.
  
          :Parameters:
              - `client_jid`: client name requested. May be `None` to allow
                any name in one of the `domains`.
              - `domains`: list of domains we can handle.
          :Types:
              - `client_jid`: `JID`
              - `domains`: `list` of `unicode`
  
          :Return: one of the jids in the certificate or `None` is no authorized
          name is found.