Neos\Flow\Session\SessionManagerInterface::getSession PHP Method

    public function getSession($sessionIdentifier);

 /**
  * Logs a user in if a session identifier is available under the given token in the token cache.
  *
  * @param string $token
  * @return void
  */
 public function tokenLoginAction($token)
 {
     $newSessionId = $this->loginTokenCache->get($token);
     $this->loginTokenCache->remove($token);
     if ($newSessionId === false) {
         $this->systemLogger->log(sprintf('Token-based login failed, non-existing or expired token %s', $token), LOG_WARNING);
         $this->redirect('index');
     }
     $this->systemLogger->log(sprintf('Token-based login succeeded, token %s', $token), LOG_DEBUG);
     $newSession = $this->sessionManager->getSession($newSessionId);
     if ($newSession->canBeResumed()) {
         $newSession->resume();
     }
     if ($newSession->isStarted()) {
         $newSession->putData('lastVisitedNode', null);
     } else {
         $this->systemLogger->log(sprintf('Failed resuming or starting session %s which was referred to in the login token %s.', $newSessionId, $token), LOG_ERR);
     }
     $this->replaceSessionCookie($newSessionId);
     $this->redirect('index', 'Backend\\Backend');
 }