code: def validate_key(self, activation_key):
          
          try:
              username = signing.loads(
                  activation_key,
                  salt=REGISTRATION_SALT,
                  max_age=settings.ACCOUNT_ACTIVATION_DAYS * 86400
              )
              return username
          except signing.SignatureExpired:
              raise ActivationError(
                  self.EXPIRED_MESSAGE,
                  code='expired'
              )
          except signing.BadSignature:
              raise ActivationError(
                  self.INVALID_KEY_MESSAGE,
                  code='invalid_key',
                  params={'activation_key': activation_key}
              )
docs: Verify that the activation key is valid and within the
          permitted activation time window, returning the username if
          valid or raising ``ActivationError`` if not.