Sessions

The Symfony HttpFoundation component has a very powerful and flexible session subsystem which is designed to provide session management that you can use to store information about the user between requests through a clear object-oriented interface using a variety of session storage drivers.

Symfony sessions are designed to replace the usage of the $_SESSION super global and native PHP functions related to manipulating the session like session_start(), session_regenerate_id(), session_id(), session_name(), and session_destroy().

Note

Sessions are only started if you read or write from it.

Installation

You need to install the HttpFoundation component to handle sessions:

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        $ composer require symfony/http-foundation
    

Basic Usage

The session is available through the Request object and the RequestStack service. Symfony injects the request_stack service in services and controllers if you type-hint an argument with RequestStack:

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        use Symfony\Component\HttpFoundation\RequestStack;

class SomeService
{
    public function __construct(
        private RequestStack $requestStack,
    ) {
        // Accessing the session in the constructor is *NOT* recommended, since
        // it might not be accessible yet or lead to unwanted side-effects
        // $this->session = $requestStack->getSession();
    }

    public function someMethod(): void
    {
        $session = $this->requestStack->getSession();

        // ...
    }
}
    

From a Symfony controller, you can also type-hint an argument with Request:

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        use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

public function index(Request $request): Response
{
    $session = $request->getSession();

    // ...
}
    

Session Attributes

PHP's session management requires the use of the $_SESSION super-global. However, this interferes with code testability and encapsulation in an OOP paradigm. To help overcome this, Symfony uses session bags linked to the session to encapsulate a specific dataset of attributes.

This approach mitigates namespace pollution within the $_SESSION super-global because each bag stores all its data under a unique namespace. This allows Symfony to peacefully co-exist with other applications or libraries that might use the $_SESSION super-global and all data remains completely compatible with Symfony's session management.

A session bag is a PHP object that acts like an array:

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        // stores an attribute for reuse during a later user request
$session->set('attribute-name', 'attribute-value');

// gets an attribute by name
$foo = $session->get('foo');

// the second argument is the value returned when the attribute doesn't exist
$filters = $session->get('filters', []);
    

Stored attributes remain in the session for the remainder of that user's session. By default, session attributes are key-value pairs managed with the AttributeBag class.

Sessions are automatically started whenever you read, write or even check for the existence of data in the session. This may hurt your application performance because all users will receive a session cookie. In order to prevent starting sessions for anonymous users, you must completely avoid accessing the session.

Note

Sessions will also be started when using features that rely on them internally, such as the CSRF protection in forms.

Flash Messages

You can store special messages, called "flash" messages, on the user's session. By design, flash messages are meant to be used exactly once: they vanish from the session automatically as soon as you retrieve them. This feature makes "flash" messages particularly great for storing user notifications.

For example, imagine you're processing a form submission:

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        use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
// ...

public function update(Request $request): Response
{
    // ...

    if ($form->isSubmitted() && $form->isValid()) {
        // do some sort of processing

        $this->addFlash(
            'notice',
            'Your changes were saved!'
        );
        // $this->addFlash() is equivalent to $request->getSession()->getFlashBag()->add()

        return $this->redirectToRoute(/* ... */);
    }

    return $this->render(/* ... */);
}
    

After processing the request, the controller sets a flash message in the session and then redirects. The message key (notice in this example) can be anything. You'll use this key to retrieve the message.

In the template of the next page (or even better, in your base layout template), read any flash messages from the session using the flashes() method provided by the Twig global app variable. Alternatively, you can use the peek() method to retrieve the message while keeping it in the bag:

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        {# templates/base.html.twig #}

{# read and display just one flash message type #}
{% for message in app.flashes('notice') %}
    <div class="flash-notice">
        {{ message }}
    </div>
{% endfor %}

{# same but without clearing them from the flash bag #}
{% for message in app.session.flashbag.peek('notice') %}
    <div class="flash-notice">
        {{ message }}
    </div>
{% endfor %}

{# read and display several types of flash messages #}
{% for label, messages in app.flashes(['success', 'warning']) %}
    {% for message in messages %}
        <div class="flash-{{ label }}">
            {{ message }}
        </div>
    {% endfor %}
{% endfor %}

{# read and display all flash messages #}
{% for label, messages in app.flashes %}
    {% for message in messages %}
        <div class="flash-{{ label }}">
            {{ message }}
        </div>
    {% endfor %}
{% endfor %}

{# or without clearing the flash bag #}
{% for label, messages in app.session.flashbag.peekAll() %}
    {% for message in messages %}
        <div class="flash-{{ label }}">
            {{ message }}
        </div>
    {% endfor %}
{% endfor %}
    

It's common to use notice, warning and error as the keys of the different types of flash messages, but you can use any key that fits your needs.

Configuration

In the Symfony framework, sessions are enabled by default. Session storage and other configuration can be controlled under the framework.session configuration in config/packages/framework.yaml:

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        # config/packages/framework.yaml
framework:
    # Enables session support. Note that the session will ONLY be started if you read or write from it.
    # Remove or comment this section to explicitly disable session support.
    session:
        # ID of the service used for session storage
        # NULL means that Symfony uses PHP default session mechanism
        handler_id: null
        # improves the security of the cookies used for sessions
        cookie_secure: auto
        cookie_samesite: lax
        storage_factory_id: session.storage.factory.native
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <!--
            Enables session support. Note that the session will ONLY be started if you read or write from it.
            Remove or comment this section to explicitly disable session support.
            handler-id: ID of the service used for session storage
                        NULL means that Symfony uses PHP default session mechanism
            cookie-secure and cookie-samesite: improves the security of the cookies used for sessions
        -->
        <framework:session handler-id="null"
                           cookie-secure="auto"
                           cookie-samesite="lax"
                           storage_factory_id="session.storage.factory.native"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Component\HttpFoundation\Cookie;
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->session()
        // Enables session support. Note that the session will ONLY be started if you read or write from it.
        // Remove or comment this section to explicitly disable session support.
        ->enabled(true)
        // ID of the service used for session storage
        // NULL means that Symfony uses PHP default session mechanism
        ->handlerId(null)
        // improves the security of the cookies used for sessions
        ->cookieSecure('auto')
        ->cookieSamesite(Cookie::SAMESITE_LAX)
        ->storageFactoryId('session.storage.factory.native')
    ;
};
    

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        use Symfony\Component\HttpFoundation\Cookie;
use Symfony\Component\HttpFoundation\Session\Attribute\AttributeBag;
use Symfony\Component\HttpFoundation\Session\Session;
use Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage;

$storage = new NativeSessionStorage([
    'cookie_secure' => 'auto',
    'cookie_samesite' => Cookie::SAMESITE_LAX,
]);
$session = new Session($storage);
    

Setting the handler_id config option to null means that Symfony will use the native PHP session mechanism. The session metadata files will be stored outside of the Symfony application, in a directory controlled by PHP. Although this usually simplifies things, some session expiration related options may not work as expected if other applications that write to the same directory have short max lifetime settings.

If you prefer, you can use the session.handler.native_file service as handler_id to let Symfony manage the sessions itself. Another useful option is save_path, which defines the directory where Symfony will store the session metadata files:

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        # config/packages/framework.yaml
framework:
    session:
        # ...
        handler_id: 'session.handler.native_file'
        save_path: '%kernel.project_dir%/var/sessions/%kernel.environment%'
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <framework:session enabled="true"
                           handler-id="session.handler.native_file"
                           save-path="%kernel.project_dir%/var/sessions/%kernel.environment%"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->session()
        // ...
        ->handlerId('session.handler.native_file')
        ->savePath('%kernel.project_dir%/var/sessions/%kernel.environment%')
    ;
};
    

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        use Symfony\Component\HttpFoundation\Cookie;
use Symfony\Component\HttpFoundation\Session\Attribute\AttributeBag;
use Symfony\Component\HttpFoundation\Session\Session;
use Symfony\Component\HttpFoundation\Session\Storage\Handler\NativeFileSessionHandler;
use Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage;

$handler = new NativeFileSessionHandler('/var/sessions');
$storage = new NativeSessionStorage([], $handler);
$session = new Session($storage);
    

Check out the Symfony config reference to learn more about the other available Session configuration options.

Caution

Symfony sessions are incompatible with php.ini directive session.auto_start = 1 This directive should be turned off in php.ini, in the web server directives or in .htaccess.

The session cookie is also available in the Response object. This is useful to get that cookie in the CLI context or when using PHP runners like Roadrunner or Swoole.

Session Idle Time/Keep Alive

There are often circumstances where you may want to protect, or minimize unauthorized use of a session when a user steps away from their terminal while logged in by destroying the session after a certain period of idle time. For example, it is common for banking applications to log the user out after just 5 to 10 minutes of inactivity. Setting the cookie lifetime here is not appropriate because that can be manipulated by the client, so we must do the expiry on the server side. The easiest way is to implement this via session garbage collection which runs reasonably frequently. The cookie_lifetime would be set to a relatively high value, and the garbage collection gc_maxlifetime would be set to destroy sessions at whatever the desired idle period is.

The other option is specifically check if a session has expired after the session is started. The session can be destroyed as required. This method of processing can allow the expiry of sessions to be integrated into the user experience, for example, by displaying a message.

Symfony records some metadata about each session to give you fine control over the security settings:

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        $session->getMetadataBag()->getCreated();
$session->getMetadataBag()->getLastUsed();
    

Both methods return a Unix timestamp (relative to the server).

This metadata can be used to explicitly expire a session on access:

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        $session->start();
if (time() - $session->getMetadataBag()->getLastUsed() > $maxIdleTime) {
    $session->invalidate();
    throw new SessionExpired(); // redirect to expired session page
}
    

It is also possible to tell what the cookie_lifetime was set to for a particular cookie by reading the getLifetime() method:

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        $session->getMetadataBag()->getLifetime();
    

The expiry time of the cookie can be determined by adding the created timestamp and the lifetime.

Configuring Garbage Collection

When a session opens, PHP will call the gc handler randomly according to the probability set by session.gc_probability / session.gc_divisor. For example if these were set to 5/100 respectively, it would mean a probability of 5%. Similarly, 3/4 would mean a 3 in 4 chance of being called, i.e. 75%.

If the garbage collection handler is invoked, PHP will pass the value stored in the php.ini directive session.gc_maxlifetime. The meaning in this context is that any stored session that was saved more than gc_maxlifetime ago should be deleted. This allows one to expire records based on idle time.

However, some operating systems (e.g. Debian) do their own session handling and set the session.gc_probability variable to 0 to stop PHP doing garbage collection. That's why Symfony now overwrites this value to 1.

If you wish to use the original value set in your php.ini, add the following configuration:

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        # config/packages/framework.yaml
framework:
    session:
        # ...
        gc_probability: null
    

You can configure these settings by passing gc_probability, gc_divisor and gc_maxlifetime in an array to the constructor of NativeSessionStorage or to the setOptions() method.

Store Sessions in a Database

Symfony stores sessions in files by default. If your application is served by multiple servers, you'll need to use a database instead to make sessions work across different servers.

Symfony can store sessions in all kinds of databases (relational, NoSQL and key-value) but recommends key-value databases like Redis to get best performance.

Store Sessions in a key-value Database (Redis)

This section assumes that you have a fully-working Redis server and have also installed and configured the phpredis extension.

You have two different options to use Redis to store sessions:

The first PHP-based option is to configure Redis session handler directly in the server php.ini file:

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        ; php.ini
session.save_handler = redis
session.save_path = "tcp://192.168.0.178:6379?auth=REDIS_PASSWORD"
    

The second option is to configure Redis sessions in Symfony. First, define a Symfony service for the connection to the Redis server:

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        # config/services.yaml
services:
    # ...
    Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler:
        arguments:
            - '@Redis'
            # you can optionally pass an array of options. The only options are 'prefix' and 'ttl',
            # which define the prefix to use for the keys to avoid collision on the Redis server
            # and the expiration time for any given entry (in seconds), defaults are 'sf_s' and null:
            # - { 'prefix': 'my_prefix', 'ttl': 600 }

    Redis:
        # you can also use \RedisArray, \RedisCluster, \Relay\Relay or \Predis\Client classes
        class: \Redis
        calls:
            - connect:
                - '%env(REDIS_HOST)%'
                - '%env(int:REDIS_PORT)%'

            # uncomment the following if your Redis server requires a password
            # - auth:
            #     - '%env(REDIS_PASSWORD)%'

            # uncomment the following if your Redis server requires a user and a password (when user is not default)
            # - auth:
            #     - ['%env(REDIS_USER)%','%env(REDIS_PASSWORD)%']
    

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        <?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 https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <!-- you can also use \RedisArray, \RedisCluster, \Relay\Relay or \Predis\Client classes -->
        <service id="Redis" class="Redis">
            <call method="connect">
                <argument>%env(REDIS_HOST)%</argument>
                <argument>%env(int:REDIS_PORT)%</argument>
            </call>

            <!-- uncomment the following if your Redis server requires a password:
            <call method="auth">
                <argument>%env(REDIS_PASSWORD)%</argument>
            </call> -->

            <!-- uncomment the following if your Redis server requires a user and a password (when user is not default):
            <call method="auth">
                <argument>%env(REDIS_USER)%</argument>
                <argument>%env(REDIS_PASSWORD)%</argument>
            </call> -->
        </service>

        <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler">
            <argument type="service" id="Redis"/>
            <!-- you can optionally pass an array of options. The only options are 'prefix' and 'ttl',
                 which define the prefix to use for the keys to avoid collision on the Redis server
                 and the expiration time for any given entry (in seconds), defaults are 'sf_s' and null:
            <argument type="collection">
                <argument key="prefix">my_prefix</argument>
                <argument key="ttl">600</argument>
            </argument> -->
        </service>
    </services>
</container>
    

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        // config/services.php
use Symfony\Component\DependencyInjection\Reference;
use Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler;

$container
    // you can also use \RedisArray, \RedisCluster, \Relay\Relay or \Predis\Client classes
    ->register('Redis', \Redis::class)
    ->addMethodCall('connect', ['%env(REDIS_HOST)%', '%env(int:REDIS_PORT)%'])
    // uncomment the following if your Redis server requires a password:
    // ->addMethodCall('auth', ['%env(REDIS_PASSWORD)%'])
    // uncomment the following if your Redis server requires a user and a password (when user is not default):
    // ->addMethodCall('auth', ['%env(REDIS_USER)%', '%env(REDIS_PASSWORD)%'])

    ->register(RedisSessionHandler::class)
    ->addArgument(
        new Reference('Redis'),
        // you can optionally pass an array of options. The only options are 'prefix' and 'ttl',
        // which define the prefix to use for the keys to avoid collision on the Redis server
        // and the expiration time for any given entry (in seconds), defaults are 'sf_s' and null:
        // ['prefix' => 'my_prefix', 'ttl' => 600],
    )
;
    

Next, use the handler_id configuration option to tell Symfony to use this service as the session handler:

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        # config/packages/framework.yaml
framework:
    # ...
    session:
        handler_id: Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <!-- ... -->
        <framework:session handler-id="Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler;
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    // ...
    $framework->session()
        ->handlerId(RedisSessionHandler::class)
    ;
};
    

Symfony will now use your Redis server to read and write the session data. The main drawback of this solution is that Redis does not perform session locking, so you can face race conditions when accessing sessions. For example, you may see an "Invalid CSRF token" error because two requests were made in parallel and only the first one stored the CSRF token in the session.

Store Sessions in a Relational Database (MariaDB, MySQL, PostgreSQL)

Symfony includes a PdoSessionHandler to store sessions in relational databases like MariaDB, MySQL and PostgreSQL. To use it, first register a new handler service with your database credentials:

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        # config/services.yaml
services:
    # ...

    Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler:
        arguments:
            - '%env(DATABASE_URL)%'

            # you can also use PDO configuration, but requires passing two arguments
            # - 'mysql:dbname=mydatabase; host=myhost; port=myport'
            # - { db_username: myuser, db_password: mypassword }
    

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        <!-- 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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <services>
        <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler">
            <argument>%env(DATABASE_URL)%</argument>

            <!-- you can also use PDO configuration, but requires passing two arguments: -->
            <!-- <argument>mysql:dbname=mydatabase; host=myhost; port=myport</argument>
                <argument type="collection">
                    <argument key="db_username">myuser</argument>
                    <argument key="db_password">mypassword</argument>
                </argument> -->
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler;

return static function (ContainerConfigurator $container): void {
    $services = $container->services();

    $services->set(PdoSessionHandler::class)
        ->args([
            env('DATABASE_URL'),
            // you can also use PDO configuration, but requires passing two arguments:
            // 'mysql:dbname=mydatabase; host=myhost; port=myport',
            // ['db_username' => 'myuser', 'db_password' => 'mypassword'],
        ])
    ;
};
    

Tip

When using MySQL as the database, the DSN defined in DATABASE_URL can contain the charset and unix_socket options as query string parameters.

Next, use the handler_id configuration option to tell Symfony to use this service as the session handler:

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        # config/packages/framework.yaml
framework:
    session:
        # ...
        handler_id: Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <!-- ... -->
        <framework:session
            handler-id="Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler;
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    // ...
    $framework->session()
        ->handlerId(PdoSessionHandler::class)
    ;
};
    

Configuring the Session Table and Column Names

The table used to store sessions is called sessions by default and defines certain column names. You can configure these values with the second argument passed to the PdoSessionHandler service:

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        # config/services.yaml
services:
    # ...

    Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler:
        arguments:
            - '%env(DATABASE_URL)%'
            - { db_table: 'customer_session', db_id_col: 'guid' }
    

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        <!-- 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
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler">
            <argument>%env(DATABASE_URL)%</argument>
            <argument type="collection">
                <argument key="db_table">customer_session</argument>
                <argument key="db_id_col">guid</argument>
            </argument>
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler;

return static function (ContainerConfigurator $container): void {
    $services = $container->services();

    $services->set(PdoSessionHandler::class)
        ->args([
            env('DATABASE_URL'),
            ['db_table' => 'customer_session', 'db_id_col' => 'guid'],
        ])
    ;
};
    

These are parameters that you can configure:

db_table (default sessions):: The name of the session table in your database;
db_username: (default: ''): The username used to connect when using the PDO configuration (when using the connection based on the DATABASE_URL env var, it overrides the username defined in the env var).
db_password: (default: ''): The password used to connect when using the PDO configuration (when using the connection based on the DATABASE_URL env var, it overrides the password defined in the env var).
db_id_col (default sess_id):: The name of the column where to store the session ID (column type: VARCHAR(128));
db_data_col (default sess_data):: The name of the column where to store the session data (column type: BLOB);
db_time_col (default sess_time):: The name of the column where to store the session creation timestamp (column type: INTEGER);
db_lifetime_col (default sess_lifetime):: The name of the column where to store the session lifetime (column type: INTEGER);
db_connection_options (default: []): An array of driver-specific connection options;
lock_mode (default: LOCK_TRANSACTIONAL): The strategy for locking the database to avoid race conditions. Possible values are LOCK_NONE (no locking), LOCK_ADVISORY (application-level locking) and LOCK_TRANSACTIONAL (row-level locking).

Preparing the Database to Store Sessions

Before storing sessions in the database, you must create the table that stores the information.

With Doctrine installed, the session table will be automatically generated when you run the make:migration command if the database targeted by doctrine is identical to the one used by this component.

Or if you prefer to create the table yourself and the table has not already been created, the session handler provides a method called createTable() to set up this table for you according to the database engine used:

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        try {
    $sessionHandlerService->createTable();
} catch (\PDOException $exception) {
    // the table could not be created for some reason
}
    

If the table already exists an exception will be thrown.

If you would rather set up the table yourself, it's recommended to generate an empty database migration with the following command:

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        $ php bin/console doctrine:migrations:generate
    

Then, find the appropriate SQL for your database below, add it to the migration file and run the migration with the following command:

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        $ php bin/console doctrine:migrations:migrate
    

If needed, you can also add this table to your schema by calling configureSchema() method in your code.

MariaDB/MySQL

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        CREATE TABLE `sessions` (
    `sess_id` VARBINARY(128) NOT NULL PRIMARY KEY,
    `sess_data` BLOB NOT NULL,
    `sess_lifetime` INTEGER UNSIGNED NOT NULL,
    `sess_time` INTEGER UNSIGNED NOT NULL,
    INDEX `sessions_sess_lifetime_idx` (`sess_lifetime`)
) COLLATE utf8mb4_bin, ENGINE = InnoDB;
    

Note

A BLOB column type (which is the one used by default by createTable()) stores up to 64 kb. If the user session data exceeds this, an exception may be thrown or their session will be silently reset. Consider using a MEDIUMBLOB if you need more space.

PostgreSQL

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        CREATE TABLE sessions (
    sess_id VARCHAR(128) NOT NULL PRIMARY KEY,
    sess_data BYTEA NOT NULL,
    sess_lifetime INTEGER NOT NULL,
    sess_time INTEGER NOT NULL
);
CREATE INDEX sessions_sess_lifetime_idx ON sessions (sess_lifetime);
    

Microsoft SQL Server

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        CREATE TABLE sessions (
    sess_id VARCHAR(128) NOT NULL PRIMARY KEY,
    sess_data NVARCHAR(MAX) NOT NULL,
    sess_lifetime INTEGER NOT NULL,
    sess_time INTEGER NOT NULL,
    INDEX sessions_sess_lifetime_idx (sess_lifetime)
);
    

Store Sessions in a NoSQL Database (MongoDB)

Symfony includes a MongoDbSessionHandler to store sessions in the MongoDB NoSQL database. First, make sure to have a working MongoDB connection in your Symfony application as explained in the DoctrineMongoDBBundle configuration article.

Then, register a new handler service for MongoDbSessionHandler and pass it the MongoDB connection as argument, and the required parameters:

database:: The name of the database
collection:: The name of the collection

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        # config/services.yaml
services:
    # ...

    Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler:
        arguments:
            - '@doctrine_mongodb.odm.default_connection'
            - { database: '%env(MONGODB_DB)%', collection: 'sessions' }
    

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        <!-- 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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <services>
        <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler">
            <argument type="service">doctrine_mongodb.odm.default_connection</argument>
            <argument type="collection">
                <argument key="database">%env('MONGODB_DB')%</argument>
                <argument key="collection">sessions</argument>
            </argument>
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler;

return static function (ContainerConfigurator $container): void {
    $services = $container->services();

    $services->set(MongoDbSessionHandler::class)
        ->args([
            service('doctrine_mongodb.odm.default_connection'),
            ['database' => '%env("MONGODB_DB")%', 'collection' => 'sessions']
        ])
    ;
};
    

Next, use the handler_id configuration option to tell Symfony to use this service as the session handler:

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        # config/packages/framework.yaml
framework:
    session:
        # ...
        handler_id: Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd
        http://symfony.com/schema/dic/symfony
        https://symfony.com/schema/dic/symfony/symfony-1.0.xsd">

    <framework:config>
        <!-- ... -->
        <framework:session
            handler-id="Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler;
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    // ...
    $framework->session()
        ->handlerId(MongoDbSessionHandler::class)
    ;
};
    

That's all! Symfony will now use your MongoDB server to read and write the session data. You do not need to do anything to initialize your session collection. However, you may want to add an index to improve garbage collection performance. Run this from the MongoDB shell:

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        use session_db
db.session.createIndex( { "expires_at": 1 }, { expireAfterSeconds: 0 } )
    

Configuring the Session Field Names

The collection used to store sessions defines certain field names. You can configure these values with the second argument passed to the MongoDbSessionHandler service:

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        # config/services.yaml
services:
    # ...

    Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler:
        arguments:
            - '@doctrine_mongodb.odm.default_connection'
            -
                database: '%env(MONGODB_DB)%'
                collection: 'sessions'
                id_field: '_guid'
                expiry_field: 'eol'
    

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        <!-- 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
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler">
            <argument type="service">doctrine_mongodb.odm.default_connection</argument>
            <argument type="collection">
                <argument key="database">%env('MONGODB_DB')%</argument>
                <argument key="collection">sessions</argument>
                <argument key="id_field">_guid</argument>
                <argument key="expiry_field">eol</argument>
            </argument>
        </service>
    </services>
</container>
    

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        // config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use Symfony\Component\HttpFoundation\Session\Storage\Handler\MongoDbSessionHandler;

return static function (ContainerConfigurator $container): void {
    $services = $container->services();

    $services->set(MongoDbSessionHandler::class)
        ->args([
            service('doctrine_mongodb.odm.default_connection'),
            [
                'database' => '%env('MONGODB_DB')%',
                'collection' => 'sessions'
                'id_field' => '_guid',
                'expiry_field' => 'eol',
            ],
        ])
    ;
};
    

These are parameters that you can configure:

id_field (default _id):: The name of the field where to store the session ID;
data_field (default data):: The name of the field where to store the session data;
time_field (default time):: The name of the field where to store the session creation timestamp;
expiry_field (default expires_at):: The name of the field where to store the session lifetime.

Migrating Between Session Handlers

If your application changes the way sessions are stored, use the MigratingSessionHandler to migrate between old and new save handlers without losing session data.

This is the recommended migration workflow:

Switch to the migrating handler, with your new handler as the write-only one. The old handler behaves as usual and sessions get written to the new one:
```
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```
```
$sessionStorage = new MigratingSessionHandler($oldSessionStorage, $newSessionStorage);
```
After your session gc period, verify that the data in the new handler is correct.
Update the migrating handler to use the old handler as the write-only one, so the sessions will now be read from the new handler. This step allows easier rollbacks:
```
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```
```
$sessionStorage = new MigratingSessionHandler($newSessionStorage, $oldSessionStorage);
```
After verifying that the sessions in your application are working, switch from the migrating handler to the new handler.

Configuring the Session TTL

Symfony by default will use PHP's ini setting session.gc_maxlifetime as session lifetime. When you store sessions in a database, you can also configure your own TTL in the framework configuration or even at runtime.

Note

Changing the ini setting is not possible once the session is started so if you want to use a different TTL depending on which user is logged in, you must do it at runtime using the callback method below.

Configure the TTL

You need to pass the TTL in the options array of the session handler you are using:

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        # config/services.yaml
services:
    # ...
    Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler:
        arguments:
            - '@Redis'
            - { 'ttl': 600 }
    

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        <!-- config/services.xml -->
<services>
    <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler">
        <argument type="service" id="Redis"/>
        <argument type="collection">
            <argument key="ttl">600</argument>
        </argument>
    </service>
</services>
    

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        // config/services.php
use Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler;

$services
    ->set(RedisSessionHandler::class)
    ->args([
        service('Redis'),
        ['ttl' => 600],
    ]);
    

Configure the TTL Dynamically at Runtime

If you would like to have a different TTL for different users or sessions for whatever reason, this is also possible by passing a callback as the TTL value. The callback will be called right before the session is written and has to return an integer which will be used as TTL.

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        # config/services.yaml
services:
    # ...
    Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler:
        arguments:
            - '@Redis'
            - { 'ttl': !closure '@my.ttl.handler' }

    my.ttl.handler:
        class: Some\InvokableClass # some class with an __invoke() method
        arguments:
            # Inject whatever dependencies you need to be able to resolve a TTL for the current session
            - '@security'
    

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        <!-- config/services.xml -->
<services>
    <service id="Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler">
        <argument type="service" id="Redis"/>
        <argument type="collection">
            <argument key="ttl" type="closure" id="my.ttl.handler"/>
        </argument>
    </service>
    <!-- some class with an __invoke() method -->
    <service id="my.ttl.handler" class="Some\InvokableClass">
        <!-- Inject whatever dependencies you need to be able to resolve a TTL for the current session -->
        <argument type="service" id="security"/>
    </service>
</services>
    

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        // config/services.php
use Symfony\Component\HttpFoundation\Session\Storage\Handler\RedisSessionHandler;

$services
    ->set(RedisSessionHandler::class)
    ->args([
        service('Redis'),
        ['ttl' => closure(service('my.ttl.handler'))],
    ]);

$services
    // some class with an __invoke() method
    ->set('my.ttl.handler', 'Some\InvokableClass')
    // Inject whatever dependencies you need to be able to resolve a TTL for the current session
    ->args([service('security')]);
    

Making the Locale "Sticky" during a User's Session

Symfony stores the locale setting in the Request, which means that this setting is not automatically saved ("sticky") across requests. But, you can store the locale in the session, so that it's used on subsequent requests.

Creating a LocaleSubscriber

Create a new event subscriber. Typically, _locale is used as a routing parameter to signify the locale, though you can determine the correct locale however you want:

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        // src/EventSubscriber/LocaleSubscriber.php
namespace App\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\RequestEvent;
use Symfony\Component\HttpKernel\KernelEvents;

class LocaleSubscriber implements EventSubscriberInterface
{
    public function __construct(
        private string $defaultLocale = 'en',
    ) {
    }

    public function onKernelRequest(RequestEvent $event): void
    {
        $request = $event->getRequest();
        if (!$request->hasPreviousSession()) {
            return;
        }

        // try to see if the locale has been set as a _locale routing parameter
        if ($locale = $request->attributes->get('_locale')) {
            $request->getSession()->set('_locale', $locale);
        } else {
            // if no explicit locale has been set on this request, use one from the session
            $request->setLocale($request->getSession()->get('_locale', $this->defaultLocale));
        }
    }

    public static function getSubscribedEvents(): array
    {
        return [
            // must be registered before (i.e. with a higher priority than) the default Locale listener
            KernelEvents::REQUEST => [['onKernelRequest', 20]],
        ];
    }
}
    

If you're using the default services.yaml configuration, you're done! Symfony will automatically know about the event subscriber and call the onKernelRequest method on each request.

To see it working, either set the _locale key on the session manually (e.g. via some "Change Locale" route & controller), or create a route with the _locale default.

You can also explicitly configure it, in order to pass in the default_locale:

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        # config/services.yaml
services:
    # ...

    App\EventSubscriber\LocaleSubscriber:
        arguments: ['%kernel.default_locale%']
        # uncomment the next line if you are not using autoconfigure
        # tags: [kernel.event_subscriber]
    

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        <!-- 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
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="App\EventSubscriber\LocaleSubscriber">
            <argument>%kernel.default_locale%</argument>

            <!-- uncomment the next line if you are not using autoconfigure -->
            <!-- <tag name="kernel.event_subscriber"/> -->
        </service>
    </services>
</container>
    

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        // config/services.php
use App\EventSubscriber\LocaleSubscriber;

$container->register(LocaleSubscriber::class)
    ->addArgument('%kernel.default_locale%')
    // uncomment the next line if you are not using autoconfigure
    // ->addTag('kernel.event_subscriber')
;
    

Now celebrate by changing the user's locale and seeing that it's sticky throughout the request.

Remember, to get the user's locale, always use the Request::getLocale method:

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        // from a controller...
use Symfony\Component\HttpFoundation\Request;

public function index(Request $request): void
{
    $locale = $request->getLocale();
}
    

Setting the Locale Based on the User's Preferences

You might want to improve this technique even further and define the locale based on the user entity of the logged in user. However, since the LocaleSubscriber is called before the FirewallListener, which is responsible for handling authentication and setting the user token on the TokenStorage, you have no access to the user which is logged in.

Suppose you have a locale property on your User entity and want to use this as the locale for the given user. To accomplish this, you can hook into the login process and update the user's session with this locale value before they are redirected to their first page.

To do this, you need an event subscriber on the LoginSuccessEvent::class event:

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        // src/EventSubscriber/UserLocaleSubscriber.php
namespace App\EventSubscriber;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpFoundation\RequestStack;
use Symfony\Component\Security\Http\Event\LoginSuccessEvent;

/**
 * Stores the locale of the user in the session after the
 * login. This can be used by the LocaleSubscriber afterwards.
 */
class UserLocaleSubscriber implements EventSubscriberInterface
{
    public function __construct(
        private RequestStack $requestStack,
    ) {
    }

    public function onLoginSuccess(LoginSuccessEvent $event): void
    {
        $user = $event->getUser();

        if (null !== $user->getLocale()) {
            $this->requestStack->getSession()->set('_locale', $user->getLocale());
        }
    }

    public static function getSubscribedEvents(): array
    {
        return [
            LoginSuccessEvent::class => 'onLoginSuccess',
        ];
    }
}
    

Caution

In order to update the language immediately after a user has changed their language preferences, you also need to update the session when you change the User entity.

Session Proxies

The session proxy mechanism has a variety of uses and this article demonstrates two common ones. Rather than using the regular session handler, you can create a custom save handler by defining a class that extends the SessionHandlerProxy class.

Then, define the class as a service. If you're using the default services.yaml configuration, that happens automatically.

Finally, use the framework.session.handler_id configuration option to tell Symfony to use your session handler instead of the default one:

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        # config/packages/framework.yaml
framework:
    session:
        # ...
        handler_id: App\Session\CustomSessionHandler
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <framework:config>
        <framework:session handler-id="App\Session\CustomSessionHandler"/>
    </framework:config>
</container>
    

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        // config/packages/framework.php
use App\Session\CustomSessionHandler;
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    // ...
    $framework->session()
        ->handlerId(CustomSessionHandler::class)
    ;
};
    

Keep reading the next sections to learn how to use the session handlers in practice to solve two common use cases: encrypt session information and define read-only guest sessions.

Encryption of Session Data

If you want to encrypt the session data, you can use the proxy to encrypt and decrypt the session as required. The following example uses the php-encryption library, but you can adapt it to any other library that you may be using:

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        // src/Session/EncryptedSessionProxy.php
namespace App\Session;

use Defuse\Crypto\Crypto;
use Defuse\Crypto\Key;
use Symfony\Component\HttpFoundation\Session\Storage\Proxy\SessionHandlerProxy;

class EncryptedSessionProxy extends SessionHandlerProxy
{
    public function __construct(
        private \SessionHandlerInterface $handler,
        private Key $key
    ) {
        parent::__construct($handler);
    }

    public function read($id): string
    {
        $data = parent::read($id);

        return Crypto::decrypt($data, $this->key);
    }

    public function write($id, $data): string
    {
        $data = Crypto::encrypt($data, $this->key);

        return parent::write($id, $data);
    }
}
    

Another possibility to encrypt session data is to decorate the session.marshaller service, which points out to MarshallingSessionHandler. You can decorate this handler with a marshaller that uses encryption, like the SodiumMarshaller.

First, you need to generate a secure key and add it to your secret store as SESSION_DECRYPTION_FILE:

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        $ php -r 'echo base64_encode(sodium_crypto_box_keypair());'
    

Then, register the SodiumMarshaller service using this key:

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        # config/services.yaml
services:

    # ...
    Symfony\Component\Cache\Marshaller\SodiumMarshaller:
        decorates: 'session.marshaller'
        arguments:
            - ['%env(file:resolve:SESSION_DECRYPTION_FILE)%']
            - '@.inner'
    

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        <!-- 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
        https://symfony.com/schema/dic/services/services-1.0.xsd"
>
    <services>
        <service id="Symfony\Component\Cache\Marshaller\SodiumMarshaller" decorates="session.marshaller">
            <argument type="collection">
                <argument>env(file:resolve:SESSION_DECRYPTION_FILE)</argument>
            </argument>
            <argument type="service" id=".inner"/>
        </service>
    </services>
</container>
    

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        // config/services.php
use Symfony\Component\Cache\Marshaller\SodiumMarshaller;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;
// ...

return function(ContainerConfigurator $container) {
    $services = $container->services();

    // ...

    $services->set(SodiumMarshaller::class)
        ->decorate('session.marshaller')
        ->args([
            [env('file:resolve:SESSION_DECRYPTION_FILE')],
            service('.inner'),
        ]);
};
    

Danger

This will encrypt the values of the cache items, but not the cache keys. Be careful not to leak sensitive data in the keys.

Read-only Guest Sessions

There are some applications where a session is required for guest users, but where there is no particular need to persist the session. In this case you can intercept the session before it is written:

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        // src/Session/ReadOnlySessionProxy.php
namespace App\Session;

use App\Entity\User;
use Symfony\Bundle\SecurityBundle\Security;
use Symfony\Component\HttpFoundation\Session\Storage\Proxy\SessionHandlerProxy;

class ReadOnlySessionProxy extends SessionHandlerProxy
{
    public function __construct(
        private \SessionHandlerInterface $handler,
        private Security $security
    ) {
        parent::__construct($handler);
    }

    public function write($id, $data): string
    {
        if ($this->getUser() && $this->getUser()->isGuest()) {
            return;
        }

        return parent::write($id, $data);
    }

    private function getUser(): ?User
    {
        $user = $this->security->getUser();
        if (is_object($user)) {
            return $user;
        }

        return null;
    }
}
    

Integrating with Legacy Applications

If you're integrating the Symfony full-stack Framework into a legacy application that starts the session with session_start(), you may still be able to use Symfony's session management by using the PHP Bridge session.

If the application has its own PHP save handler, you can specify null for the handler_id:

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        # config/packages/framework.yaml
framework:
    session:
        storage_factory_id: session.storage.factory.php_bridge
        handler_id: ~
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <framework:config>
        <framework:session storage-factory-id="session.storage.factory.php_bridge"
            handler-id="null"
        />
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->session()
        ->storageFactoryId('session.storage.factory.php_bridge')
        ->handlerId(null)
    ;
};
    

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        use Symfony\Component\HttpFoundation\Session\Session;
use Symfony\Component\HttpFoundation\Session\Storage\PhpBridgeSessionStorage;

// legacy application configures session
ini_set('session.save_handler', 'files');
ini_set('session.save_path', '/tmp');
session_start();

// Get Symfony to interface with this existing session
$session = new Session(new PhpBridgeSessionStorage());

// symfony will now interface with the existing PHP session
$session->start();
    

Otherwise, if the problem is that you cannot avoid the application starting the session with session_start(), you can still make use of a Symfony based session save handler by specifying the save handler as in the example below:

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        # config/packages/framework.yaml
framework:
    session:
        storage_factory_id: session.storage.factory.php_bridge
        handler_id: session.handler.native_file
    

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        <!-- config/packages/framework.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"
    xmlns:framework="http://symfony.com/schema/dic/symfony"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <framework:config>
        <framework:session storage-id="session.storage.php_bridge"
            handler-id="session.storage.native_file"
        />
    </framework:config>
</container>
    

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        // config/packages/framework.php
use Symfony\Config\FrameworkConfig;

return static function (FrameworkConfig $framework): void {
    $framework->session()
        ->storageFactoryId('session.storage.factory.php_bridge')
        ->handlerId('session.storage.native_file')
    ;
};
    

Note

If the legacy application requires its own session save handler, do not override this. Instead set handler_id: ~. Note that a save handler cannot be changed once the session has been started. If the application starts the session before Symfony is initialized, the save handler will have already been set. In this case, you will need handler_id: ~. Only override the save handler if you are sure the legacy application can use the Symfony save handler without side effects and that the session has not been started before Symfony is initialized.

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

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