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 or trying to understand a bug a user sees that you can't reproduce).

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

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# app/config/security.yml
security:
    # ...

    firewalls:
        main:
            # ...
            switch_user: true

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<!-- app/config/security.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<srv:container xmlns="http://symfony.com/schema/dic/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:srv="http://symfony.com/schema/dic/services"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <config>
        <!-- ... -->

        <firewall name="main">
            <!-- ... -->
            <switch-user />
        </firewall>
    </config>
</srv:container>

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// app/config/security.php
$container->loadFromExtension('security', array(
    // ...

    'firewalls' => array(
        'main'=> array(
            // ...
            'switch_user' => true,
        ),
    ),
));

To switch to another user, just add a query string with the _switch_user parameter and the username 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

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 %}

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;

$authorizationChecker = $this->get('security.authorization_checker');
$tokenStorage = $this->get('security.token_storage');

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

Of course, this feature needs to be made available to a small 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. For extra security, you can also change the query parameter name via the parameter setting:

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# app/config/security.yml
security:
    # ...

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

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<!-- app/config/security.xml -->
<?xml version="1.0" encoding="UTF-8"?>
<srv:container xmlns="http://symfony.com/schema/dic/security"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:srv="http://symfony.com/schema/dic/services"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">
    <config>
        <!-- ... -->

        <firewall name="main">
            <!-- ... -->
            <switch-user role="ROLE_ADMIN" parameter="_want_to_be_this_user" />
        </firewall>
    </config>
</srv:container>

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// app/config/security.php
$container->loadFromExtension('security', array(
    // ...

    'firewalls' => array(
        'main'=> array(
            // ...
            'switch_user' => array(
                'role' => 'ROLE_ADMIN',
                'parameter' => '_want_to_be_this_user',
            ),
        ),
    ),
));

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# app/config/services.yml
services:
    app.switch_user_listener:
        class: AppBundle\EventListener\SwitchUserListener
        tags:
            - { name: kernel.event_listener, event: security.switch_user, method: onSwitchUser }

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<!-- app/config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd"
>
    <services>
        <service id="app.switch_user_listener"
            class="AppBundle\EventListener\SwitchUserListener"
        >
            <tag name="kernel.event_listener"
                event="security.switch_user"
                method="onSwitchUser"
            />
        </service>
    </services>
</container>

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// app/config/services.php
use AppBundle\EventListener\SwitchUserListener;

$container
    ->register('app.switch_user_listener', SwitchUserListener::class)
    ->addTag('kernel.event_listener', array(
        'event' => 'security.switch_user',
        'method' => 'onSwitchUser',
    ))
;

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// src/AppBundle/EventListener/SwitchUserListener.php
namespace AppBundle\EventListener;

use Symfony\Component\Security\Http\Event\SwitchUserEvent;

class SwitchUserListener
{
    public function onSwitchUser(SwitchUserEvent $event)
    {
        $event->getRequest()->getSession()->set(
            '_locale',
            $event->getTargetUser()->getLocale()
        );
    }
}