docs: def handle_validate_token(self, req):
          """Handles the GET v2/.token/<token> call for validating a token, usually
          called by a service like Swift.
  
          On a successful validation, X-Auth-TTL will be set for how much longer
          this token is valid and X-Auth-Groups will contain a comma separated
          list of groups the user belongs to.
  
          The first group listed will be a unique identifier for the user the
          token represents.
  
          .reseller_admin is a special group that indicates the user should be
          allowed to do anything on any account.
  
          :param req: The swob.Request to process.
          :returns: swob.Response, 2xx on success with data set as explained
                    above.
          """
          token = req.path_info_pop()
          if req.path_info or not token.startswith(self.reseller_prefix):
              return HTTPBadRequest(request=req)
          expires = groups = None
          memcache_client = cache_from_env(req.environ)
          if memcache_client:
              memcache_key = '%s/auth/%s' % (self.reseller_prefix, token)
              cached_auth_data = memcache_client.get(memcache_key)
              if cached_auth_data:
                  expires, groups = cached_auth_data
                  if expires < time():
                      groups = None
          if not groups:
              object_name = self._get_concealed_token(token)
              path = quote('/v1/%s/.token_%s/%s' %
                           (self.auth_account, object_name[-1], object_name))
              resp = self.make_pre_authed_request(
                  req.environ, 'GET', path).get_response(self.app)
              if resp.status_int // 100 != 2:
                  return HTTPNotFound(request=req)
              detail = json.loads(resp.body)
              expires = detail['expires']
              if expires < time():
                  self.make_pre_authed_request(
                      req.environ, 'DELETE', path).get_response(self.app)
                  return HTTPNotFound(request=req)
              groups = [g['name'] for g in detail['groups']]
              if '.admin' in groups:
                  groups.remove('.admin')
                  groups.append(detail['account_id'])
              groups = ','.join(groups)
          return HTTPNoContent(headers={'X-Auth-TTL': expires - time(),
                                        'X-Auth-Groups': groups})