With Symfony2 the firewall comes with a built in feature: impersonate a user. We’ve been using impersonation as an admin tool for about 5 years as it is very effective for troubleshooting. When a user files a support ticket saying something isn’t showing properly to them or they are getting random errors it is very easy to just quickly switch to that user and see what they are seeing. As with all features, this one may not be appropriate for your application if your user expects no administrative staff to have access to his or her account.
While Symfony’s built in impersonation feature is a great step up from having to build it by hand, it still can be a bit more friendly. We’ve seen two additional functions we wanted the impersonation to handle. First, we wanted it to on exit from impersonating the user returns the user to where the user first started to impersonating. Currently it just brings you back to wherever you link the user. Second, if already impersonating a user and trying to start to impersonate another, we didn’t want it to throw an error but to quietly switch you. This functionality could lead to unwanted circumstances if an impersonating user believes they can impersonate another user, and then slowly just keep exiting impersonation of each user and go back up the chain they went down. However, in our situation the time admins hit this was when they’d impersonate one user, realize they clicked the wrong one, click back and try to impersonate a different user. As the browser uses it’s cached page when the user hits back they see the list of users as if they were an admin and can click on the correct user. If they do this they are hit with a 500 error, “You are already switched to X user”.
For both of our goals we overrode the built in switch user class. It is really easy to override, as all you need to do is specify in your parameters.yml “security.authentication.switchuser_listener.class: My\AppBundle\Listener\SwitchUser”. We used the built in class as our starting template: https://github.com/symfony/symfony/blob/2.5/src/Symfony/Component/Security/Http/Firewall/SwitchUserListener.php Our final class ended looking like:
<?php
namespace My\AppBundle\Listener;
use Symfony\Component\Security\Core\Exception\AccessDeniedException;
use Symfony\Component\Security\Core\SecurityContextInterface;
use Symfony\Component\Security\Core\User\UserProviderInterface;
use Symfony\Component\Security\Core\User\UserCheckerInterface;
use Symfony\Component\Security\Core\Authorization\AccessDecisionManagerInterface;
use Psr\Log\LoggerInterface;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\Security\Core\Exception\AuthenticationException;
use Symfony\Component\HttpFoundation\RedirectResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Security\Core\Role\SwitchUserRole;
use Symfony\Component\Security\Core\Authentication\Token\UsernamePasswordToken;
use Symfony\Component\Security\Core\Exception\AuthenticationCredentialsNotFoundException;
use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
use Symfony\Component\Security\Http\Event\SwitchUserEvent;
use Symfony\Component\Security\Http\Firewall\ListenerInterface;
use Symfony\Component\Security\Http\SecurityEvents;
use Symfony\Component\EventDispatcher\EventDispatcherInterface;
/**
* Based on built in Symfony 2 SwitchUserListener class. Modified to allow:
* 1. Redirect user on exit back to original impersonation url if one exists
* 2. Allow user to impersonate different user if they are already impersonating a user.
*/
class SwitchUserListener implements ListenerInterface
{
private $securityContext;
private $provider;
private $userChecker;
private $providerKey;
private $accessDecisionManager;
private $usernameParameter;
private $role;
private $logger;
private $dispatcher;
// Used to disable the URI redirect in case user is already impersonating one user and trying to switch to another.
private $useOverrideUri;
/**
* Constructor.
*/
public function __construct(SecurityContextInterface $securityContext, UserProviderInterface $provider, UserCheckerInterface $userChecker, $providerKey, AccessDecisionManagerInterface $accessDecisionManager, LoggerInterface $logger = null, $usernameParameter = '_switch_user', $role = 'ROLE_ALLOWED_TO_SWITCH', EventDispatcherInterface $dispatcher = null)
{
if (empty($providerKey)) {
throw new \InvalidArgumentException('$providerKey must not be empty.');
}
$this->securityContext = $securityContext;
$this->provider = $provider;
$this->userChecker = $userChecker;
$this->providerKey = $providerKey;
$this->accessDecisionManager = $accessDecisionManager;
$this->usernameParameter = $usernameParameter;
$this->role = $role;
$this->logger = $logger;
$this->dispatcher = $dispatcher;
$this->useOverrideUri = true;
}
/**
* Handles the switch to another user.
*
* @param GetResponseEvent $event A GetResponseEvent instance
*
* @throws \LogicException if switching to a user failed
*/
public function handle(GetResponseEvent $event)
{
$request = $event->getRequest();
if (!$request->get($this->usernameParameter)) {
return;
}
if ('_exit' === $request->get($this->usernameParameter)) {
$this->securityContext->setToken($this->attemptExitUser($request));
} else {
try {
$this->securityContext->setToken($this->attemptSwitchUser($request));
} catch (AuthenticationException $e) {
throw new \LogicException(sprintf('Switch User failed: "%s"', $e->getMessage()));
}
}
$session = $request->getSession();
$request->query->remove($this->usernameParameter);
$overrideUri = $session->get('onSwitchURI',null);
if($request->get('returnTo'))
{
$session->set('onSwitchURI',$request->get('returnTo'));
$request->query->remove('returnTo');
}
else
$session->remove('onSwitchURI');
$request->server->set('QUERY_STRING', http_build_query($request->query->all()));
$response = new RedirectResponse($this->useOverrideUri && $overrideUri ? $overrideUri : $request->getUri(), 302);
$event->setResponse($response);
}
/**
* Attempts to switch to another user.
*
* @param Request $request A Request instance
*
* @return TokenInterface|null The new TokenInterface if successfully switched, null otherwise
*
* @throws \LogicException
* @throws AccessDeniedException
*/
private function attemptSwitchUser(Request $request)
{
$token = $this->securityContext->getToken();
$originalToken = $this->getOriginalToken($token);
if (false !== $originalToken) {
if ($token->getUsername() === $request->get($this->usernameParameter)) {
return $token;
} else {
// User is impersonating someone, they are trying to switch directly to another user, make sure original user has access.
if (false === $this->accessDecisionManager->decide($originalToken, [$this->role])){
throw new AccessDeniedException();
}
// User has a return url, most likely to admin area, as they are just trying to reimpersonate non-admin redirect to default.
$this->useOverrideUri = false;
}
}
else if (false === $this->accessDecisionManager->decide($token, [$this->role])) {
throw new AccessDeniedException();
}
$username = $request->get($this->usernameParameter);
if (null !== $this->logger) {
$this->logger->info(sprintf('Attempt to switch to user "%s"', $username));
}
$user = $this->provider->loadUserByUsername($username);
$this->userChecker->checkPostAuth($user);
$roles = $user->getRoles();
// If there is an original token, only let them switch back to that user.
if($originalToken)
$roles[] = new SwitchUserRole('ROLE_PREVIOUS_ADMIN', $originalToken);
else
$roles[] = new SwitchUserRole('ROLE_PREVIOUS_ADMIN', $this->securityContext->getToken());
$token = new UsernamePasswordToken($user, $user->getPassword(), $this->providerKey, $roles);
if (null !== $this->dispatcher) {
$switchEvent = new SwitchUserEvent($request, $token->getUser());
$this->dispatcher->dispatch(SecurityEvents::SWITCH_USER, $switchEvent);
}
return $token;
}
/**
* Attempts to exit from an already switched user.
*
* @param Request $request A Request instance
*
* @return TokenInterface The original TokenInterface instance
*
* @throws AuthenticationCredentialsNotFoundException
*/
private function attemptExitUser(Request $request)
{
if (false === $original = $this->getOriginalToken($this->securityContext->getToken())) {
throw new AuthenticationCredentialsNotFoundException('Could not find original Token object.');
}
if (null !== $this->dispatcher) {
$switchEvent = new SwitchUserEvent($request, $original->getUser());
$this->dispatcher->dispatch(SecurityEvents::SWITCH_USER, $switchEvent);
}
return $original;
}
/**
* Gets the original Token from a switched one.
*
* @param TokenInterface $token A switched TokenInterface instance
*
* @return TokenInterface|false The original TokenInterface instance, false if the current TokenInterface is not switched
*/
private function getOriginalToken(TokenInterface $token)
{
foreach ($token->getRoles() as $role) {
if ($role instanceof SwitchUserRole) {
return $role->getSource();
}
}
return false;
}
}
Here are the specifics on what everything we did and why.
First feature: Redirecting the user on exiting impersonating a user to where they originally started impersonating them. As we didn’t want to go around our entire application updating logic for the exit impersonation links if we decided to later change the behavior, we decided to build the redirect into the class itself. We didn’t want to rely on the user’s browser referrer header, so instead we decided to on the links to impersonate a user to include a “returnTo” parameter. This parameter is set to the current URI (app.request.uri). At line 97 we save the returnTo parameter to the session, for later use. On line 93, as a user is switching (in this case exiting) a user, if the session has a stored “returnTo” URL, we assign it to the “$overrideURI” variable. On line 107 we have a bit of logic on if we redirect them to the default route or the “returnTo” URL. The reason for the additional “$this->useOverrideURI” variable on this line is for our second feature of switching between users when you are already impersonating one. As the logic all runs through the same routine, if you are simply switching to a new user from an already impersonated one, we don’t want to redirect you back to your original URL when you started all the impersonating, so we disregard the redirect in this case and redirect to the default route. An example of this is admin impersonates user A, then wants to impersonate user B. Upon impersonating user B, the admin does not want to be redirected back to the admin dashboard (the sessions returnTo URL), but to where the impersonate user link is pointing to (User B homepage).
Second feature: Allow users to impersonate a different user while already impersonating another. One Line 134 is where the original SwitchUserListener would usually throw a 500 error as you are already impersonating a user. Instead, we make sure that the original token has the appropriate permissions, if so it will not throw an exception. Line 159 is the other main update for this feature. If you are already impersonating a user and try to impersonate another user, upon exiting you want to go back to your original user. Now if a original impersonation token (user) exists, we keep that as the user you’ll be switched to when you exit the impersonation.
