How to use Passwordless Login Link Authentication

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How to use Passwordless Login Link Authentication

Login links, also called "magic links", are a passwordless authentication mechanism. Whenever a user wants to login, a new link is generated and sent to them (e.g. using an email). The link fully authenticates the user in the application when clicking on it.

This authentication method can help you eliminate most of the customer support related to authentication (e.g. I forgot my password, how can I change or reset my password, etc.)

Note

Login links are only supported by Symfony when using the authenticator system. Before using this authenticator, make sure you have enabled it with enable_authenticator_manager: true in your security.yaml file.

This guide assumes you have setup security and have created a user object in your application. Follow the main security guide if this is not yet the case.

The login link authenticator is configured using the login_link option under the firewall. You must configure a check_route and signature_properties when enabling this authenticator:

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# config/packages/security.yaml
security:
    firewalls:
        main:
            login_link:
                check_route: login_check
                signature_properties: ['id']

The signature_properties are used to create a signed URL. This must contain at least one property of your User object that uniquely identifies this user (e.g. the user ID). Read more about this setting further down below.

The check_route must be an existing route and it will be used to generate the login link that will authenticate the user. You don't need a controller (or it can be empty) because the login link authenticator will intercept requests to this route:

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// src/Controller/SecurityController.php
namespace App\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\Routing\Annotation\Route;

class SecurityController extends AbstractController
{
    /**
     * @Route("/login_check", name="login_check")
     */
    public function check()
    {
        throw new \LogicException('This code should never be reached');
    }
}

Now that the authenticator is able to check the login links, you must create a page where a user can request a login link and log in to your website.

The login link can be generated using the LoginLinkHandlerInterface. The correct login link handler is autowired for you when type-hinting for this interface:

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// src/Controller/SecurityController.php
namespace App\Controller;

use App\Repository\UserRepository;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Routing\Annotation\Route;
use Symfony\Component\Security\Http\LoginLink\LoginLinkHandlerInterface;

class SecurityController extends AbstractController
{
    /**
     * @Route("/login", name="login")
     */
    public function requestLoginLink(LoginLinkHandlerInterface $loginLinkHandler, UserRepository $userRepository, Request $request)
    {
        // check if login form is submitted
        if ($request->isMethod('POST')) {
            // load the user in some way (e.g. using the form input)
            $email = $request->request->get('email');
            $user = $userRepository->findOneBy(['email' => $email]);

            // create a login link for $user this returns an instance
            // of LoginLinkDetails
            $loginLinkDetails = $loginLinkHandler->createLoginLink($user);
            $loginLink = $loginLinkDetails->getUrl();

            // ... send the link and return a response (see next section)
        }

        // if it's not submitted, render the "login" form
        return $this->render('security/login.html.twig');
    }

    // ...
}
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{# templates/security/login.html.twig #}
{% extends 'base.html.twig' %}

{% block body %}
<form action="{{ path('login') }}" method="POST">
    <input type="email" name="email">
    <button type="submit">Send Login Link</button>
</form>
{% endblock %}

In this controller, the user is submitting their e-mail address to the controller. Based on this property, the correct user is loaded and a login link is created using createLoginLink().

Caution

It is important to send this link to the user and not show it directly, as that would allow anyone to login. For instance, use the mailer component to mail the login link to the user. Or use the component to send an SMS to the user's device.

Now the link is created, it needs to be send to the user. Anyone with the link is able to login as this user, so you need to make sure to send it to a known device of them (e.g. using e-mail or SMS).

You can send the link using any library or method. However the login link authenticator provides integration with the Notifier component. Use the special LoginLinkNotification to create a notification and send it to the user's email address or phone number:

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// src/Controller/SecurityController.php

// ...
use Symfony\Component\Notifier\NotifierInterface;
use Symfony\Component\Notifier\Recipient\Recipient;
use Symfony\Component\Security\Http\LoginLink\LoginLinkNotification;

class SecurityController extends AbstractController
{
    /**
     * @Route("/login", name="login")
     */
    public function requestLoginLink(NotifierInterface $notifier, LoginLinkHandlerInterface $loginLinkHandler, UserRepository $userRepository, Request $request)
    {
        if ($request->isMethod('POST')) {
            $email = $request->request->get('email');
            $user = $userRepository->findOneBy(['email' => $email]);

            $loginLinkDetails = $loginLinkHandler->createLoginLink($user);

            // create a notification based on the login link details
            $notification = new LoginLinkNotification(
                $loginLinkDetails,
                'Welcome to MY WEBSITE!' // email subject
            );
            // create a recipient for this user
            $recipient = new Recipient($user->getEmail());

            // send the notification to the user
            $notifier->send($notification, $recipient);

            // render a "Login link is sent!" page
            return $this->render('security/login_link_sent.html.twig');
        }

        return $this->render('security/login.html.twig');
    }

    // ...
}

Note

This integration requires the Notifier and Mailer components to be installed and configured. Install all required packages using:

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$ composer require symfony/mailer symfony/notifier \
    symfony/twig-bundle twig/extra-bundle \
    twig/cssinliner-extra twig/inky-extra

This will send an email like this to the user:

Tip

You can customize this e-mail template by extending the LoginLinkNotification and configuring another htmlTemplate:

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// src/Notifier/CustomLoginLinkNotification
namespace App\Notifier;

use Symfony\Component\Security\Http\LoginLink\LoginLinkNotification;

class CustomLoginLinkNotification extends LoginLinkNotification
{
    public function asEmailMessage(EmailRecipientInterface $recipient, string $transport = null): ?EmailMessage
    {
        $emailMessage = parent::asEmailMessage($recipient, $transport);

        // get the NotificationEmail object and override the template
        $email = $emailMessage->getMessage();
        $email->htmlTemplate('emails/custom_login_link_email.html.twig');

        return $emailMessage;
    }
}

Then, use this new CustomLoginLinkNotification in the controller instead.

Important Considerations

Login links are a convenient way of authenticating users, but it is also considered less secure than a traditional username and password form. It is not recommended to use login links in security critical applications.

However, the implementation in Symfony does have a couple extension points to make the login links more secure. In this section, the most important configuration decisions are discussed:

It is important for login links to have a limited lifetime. This reduces the risk that someone can intercept the link and use it to login as somebody else. By default, Symfony defines a lifetime of 10 minutes (600 seconds). You can customize this using the lifetime option:

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# config/packages/security.yaml
security:
    firewalls:
        main:
            login_link:
                check_route: login_check
                # lifetime in seconds
                lifetime: 300

Symfony uses signed URLs to implement login links. The advantage of this is that valid links do not have to be stored in a database. The signed URLs allow Symfony to still invalidate already sent login links when important information changes (e.g. a user's email address).

The signed URL contains 3 parameters:

expires
The UNIX timestamp when the link expires.
user
The value returned from $user->getUserIdentifier() for this user.
hash
A hash of expires, user and any configured signature properties. Whenever these change, the hash changes and previous login links are invalidated.

You can add more properties to the hash by using the signature_properties option:

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# config/packages/security.yaml
security:
    firewalls:
        main:
            login_link:
                check_route: login_check
                signature_properties: [id, email]

The properties are fetched from the user object using the PropertyAccess component (e.g. using getEmail() or a public $email property in this example).

Tip

You can also use the signature properties to add very advanced invalidating logic to your login links. For instance, if you store a $lastLinkRequestedAt property on your users that you update in the requestLoginLink() controller, you can invalidate all login links whenever a user requests a new link.

It is a common characteristic of login links to limit the number of times it can be used. Symfony can support this by storing used login links in the cache. Enable this support by setting the max_uses option:

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# config/packages/security.yaml
security:
    firewalls:
        main:
            login_link:
                check_route: login_check
                # only allow the link to be used 3 times
                max_uses: 3

                # optionally, configure the cache pool
                #used_link_cache: 'cache.redis'

Make sure there is enough space left in the cache, otherwise invalid links can no longer be stored (and thus become valid again). Expired invalid links are automatically removed from the cache.

The cache pools are not cleared by the cache:clear command, but removing var/cache/ manually may remove the cache if the cache component is configured to store its cache in that location. Read the Cache guide for more information.

When setting max_uses to 1, you must take extra precautions to make it work as expected. Email providers and browsers often load a preview of the links, meaning that the link is already invalidated by the preview loader.

In order to solve this issue, first set the check_post_only option let the authenticator only handle HTTP POST methods:

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# config/packages/security.yaml
security:
    firewalls:
        main:
            login_link:
                check_route: login_check
                check_post_only: true
                max_uses: 1

Then, use the check_route controller to render a page that lets the user create this POST request (e.g. by clicking a button):

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// src/Controller/SecurityController.php
namespace App\Controller;

// ...
use Symfony\Component\Routing\Generator\UrlGeneratorInterface;

class SecurityController extends AbstractController
{
    /**
     * @Route("/login_check", name="login_check")
     */
    public function check(Request $request)
    {
        // get the login link query parameters
        $expires = $request->query->get('expires');
        $username = $request->query->get('user');
        $hash = $request->query->get('hash');

        // and render a template with the button
        return $this->render('security/process_login_link.html.twig', [
            'expires' => $expires,
            'user' => $username,
            'hash' => $hash,
        ]);
    }
}
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{# templates/security/process_login_link.html.twig #}
{% extends 'base.html.twig' %}

{% block body %}
    <h2>Hi! You are about to login to ...</h2>

    <!-- for instance, use a form with hidden fields to
         create the POST request --->
    <form action="{{ path('login_check') }}" method="POST">
        <input type="hidden" name="expires" value="{{ expires }}">
        <input type="hidden" name="user" value="{{ user }}">
        <input type="hidden" name="hash" value="{{ hash }}">

        <button type="submit">Continue</button>
    </form>
{% endblock %}

Customizing the Success Handler

Sometimes, the default success handling does not fit your use-case (e.g. when you need to generate and return an API key). To customize how the success handler behaves, create your own handler as a class that implements AuthenticationSuccessHandlerInterface:

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// src/Security/Authentication/AuthenticationSuccessHandler.php
namespace App\Security\Authentication;

use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
use Symfony\Component\Security\Http\Authentication\AuthenticationSuccessHandlerInterface;

class AuthenticationSuccessHandler implements AuthenticationSuccessHandlerInterface
{
    public function onAuthenticationSuccess(Request $request, TokenInterface $token): JsonResponse
    {
        $user = $token->getUser();
        $userApiToken = $user->getApiToken();

        return new JsonResponse(['apiToken' => 'userApiToken']);
    }
}

Then, configure this service ID as the success_handler:

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# config/packages/security.yaml
security:
    firewalls:
        main:
            login_link:
                check_route: login_check
                lifetime: 600
                max_uses: 1
                success_handler: App\Security\Authentication\AuthenticationSuccessHandler

Tip

If you want to customize the default failure handling, use the failure_handler option and create a class that implements AuthenticationFailureHandlerInterface.

5.3

The possibility to customize the login link was introduced in Symfony 5.3.

The createLoginLink() method accepts a second optional argument to pass the Request object used when generating the login link. This allows to customize features such as the locale used to generate the link:

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// src/Controller/SecurityController.php
namespace App\Controller;

// ...
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Security\Http\LoginLink\LoginLinkHandlerInterface;

class SecurityController extends AbstractController
{
    /**
     * @Route("/login", name="login")
     */
    public function requestLoginLink(LoginLinkHandlerInterface $loginLinkHandler, Request $request)
    {
        // check if login form is submitted
        if ($request->isMethod('POST')) {
            // ... load the user in some way

            // clone and customize Request
            $userRequest = clone $request;
            $userRequest->setLocale($user->getLocale() ?? $request->getDefaultLocale());

            // create a login link for $user (this returns an instance of LoginLinkDetails)
            $loginLinkDetails = $loginLinkHandler->createLoginLink($user, $userRequest);
            $loginLink = $loginLinkDetails->getUrl();

            // ...
        }

        return $this->render('security/login.html.twig');
    }

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