How to Impersonate a User

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How to Impersonate a User

Sometimes, it's useful to be able to switch from one user to another without having to log out and log in again (for instance when you are debugging something a user sees that you can't reproduce).

Caution

User impersonation is not compatible with some authentication mechanisms (e.g. REMOTE_USER) where the authentication information is expected to be sent on each request.

Impersonating the user can be done by activating the switch_user firewall listener:

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# config/packages/security.yaml
security:
    # ...

    firewalls:
        main:
            # ...
            switch_user: true

To switch to another user, add a query string with the _switch_user parameter and the username (or whatever field our user provider uses to load users) as the value to the current URL:

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http://example.com/somewhere?_switch_user=thomas

To switch back to the original user, use the special _exit username:

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http://example.com/somewhere?_switch_user=_exit

This feature is only available to users with a special role called ROLE_ALLOWED_TO_SWITCH. Using role_hierarchy is a great way to give this role to the users that need it.

Knowing When Impersonation Is Active

During impersonation, the user is provided with a special role called ROLE_PREVIOUS_ADMIN. In a template, for instance, this role can be used to show a link to exit impersonation:

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{% if is_granted('ROLE_PREVIOUS_ADMIN') %}
    <a href="{{ path('homepage', {'_switch_user': '_exit'}) }}">Exit impersonation</a>
{% endif %}

Finding the Original User

In some cases, you may need to get the object that represents the impersonator user rather than the impersonated user. Use the following snippet to iterate over the user's roles until you find one that is a SwitchUserRole object:

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use Symfony\Component\Security\Core\Role\SwitchUserRole;
use Symfony\Component\Security\Core\Security;
// ...

public class SomeService
{
    private $security;

    public function __construct(Security $security)
    {
        $this->security = $security;
    }

    public function someMethod()
    {
        // ...

        if ($this->security->isGranted('ROLE_PREVIOUS_ADMIN')) {
            foreach ($this->security->getToken()->getRoles() as $role) {
                if ($role instanceof SwitchUserRole) {
                    $impersonatorUser = $role->getSource()->getUser();
                    break;
                }
            }
        }
    }
}

Controlling the Query Parameter

This feature needs to be available only to a restricted group of users. By default, access is restricted to users having the ROLE_ALLOWED_TO_SWITCH role. The name of this role can be modified via the role setting. You can also adjust the query parameter name via the parameter setting:

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# config/packages/security.yaml
security:
    # ...

    firewalls:
        main:
            # ...
            switch_user: { role: ROLE_ADMIN, parameter: _want_to_be_this_user }

Limiting User Switching

If you need more control over user switching, you can use a security voter. First, configure switch_user to check for some new, custom attribute. This can be anything, but cannot start with ROLE_ (to enforce that only your voter will) be called:

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# config/packages/security.yaml
security:
    # ...

    firewalls:
        main:
            # ...
            switch_user: { role: CAN_SWITCH_USER }

Then, create a voter class that responds to this role and includes whatever custom logic you want:

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namespace App\Security\Voter;

use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
use Symfony\Component\Security\Core\Authorization\Voter\Voter;
use Symfony\Component\Security\Core\Security;
use Symfony\Component\Security\Core\User\UserInterface;

class SwitchToCustomerVoter extends Voter
{
    private $security;

    public function __construct(Security $security)
    {
        $this->security = $security;
    }

    protected function supports($attribute, $subject)
    {
        return in_array($attribute, ['CAN_SWITCH_USER'])
            && $subject instanceof UserInterface;
    }

    protected function voteOnAttribute($attribute, $subject, TokenInterface $token)
    {
        $user = $token->getUser();
        // if the user is anonymous or if the subject is not a user, do not grant access
        if (!$user instanceof UserInterface || !$subject instanceof UserInterface) {
            return false;
        }

        // you can still check for ROLE_ALLOWED_TO_SWITCH
        if ($this->security->isGranted('ROLE_ALLOWED_TO_SWITCH')) {
            return true;
        }

        // check for any roles you want
        if ($this->security->isGranted('ROLE_TECH_SUPPORT')) {
            return true;
        }

        /*
         * or use some custom data from your User object
        if ($user->isAllowedToSwitch()) {
            return true;
        }
        */

        return false;
    }
}

That's it! When switching users, your voter now has full control over whether or not this is allowed. If your voter isn't called, see How to Use Voters to Check User Permissions.

Events

The firewall dispatches the security.switch_user event right after the impersonation is completed. The SwitchUserEvent is passed to the listener, and you can use this to get the user that you are now impersonating.

The Making the Locale "Sticky" during a User's Session article does not update the locale when you impersonate a user. If you do want to be sure to update the locale when you switch users, add an event subscriber on this event:

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// src/EventListener/SwitchUserSubscriber.php
namespace App\EventListener;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Security\Http\Event\SwitchUserEvent;
use Symfony\Component\Security\Http\SecurityEvents;

class SwitchUserSubscriber implements EventSubscriberInterface
{
    public function onSwitchUser(SwitchUserEvent $event)
    {
        $request = $event->getRequest();

        if ($request->hasSession() && ($session = $request->getSession())) {
            $session->set(
                '_locale',
                // assuming your User has some getLocale() method
                $event->getTargetUser()->getLocale()
            );
        }
    }

    public static function getSubscribedEvents()
    {
        return [
            // constant for security.switch_user
            SecurityEvents::SWITCH_USER => 'onSwitchUser',
        ];
    }
}

That's it! If you're using the default services.yaml configuration, Symfony will automatically discover your service and call onSwitchUser whenever a switch user occurs.

For more details about event subscribers, see Events and Event Listeners.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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