How to Create a Custom Authentication System with Guard

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Read the updated version of this page for Symfony 7.2 (the current stable version).

Whether you need to build a traditional login form, an API token authentication system or you need to integrate with some proprietary single-sign-on system, the Guard component can make it easy... and fun!

In this example, you'll build an API token authentication system and learn how to work with Guard.

Create a User and a User Provider

No matter how you authenticate, you need to create a User class that implements UserInterface and configure a user provider. In this example, users are stored in the database via Doctrine, and each user has an apiKey property they use to access their account via the API:

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// src/AppBundle/Entity/User.php
namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Security\Core\User\UserInterface;

/**
 * @ORM\Entity
 * @ORM\Table(name="`user`")
 */
class User implements UserInterface
{
    /**
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", unique=true)
     */
    private $username;

    /**
     * @ORM\Column(type="string", unique=true)
     */
    private $apiKey;

    public function getUsername()
    {
        return $this->username;
    }

    public function getRoles()
    {
        return ['ROLE_USER'];
    }

    public function getPassword()
    {
    }
    public function getSalt()
    {
    }
    public function eraseCredentials()
    {
    }

    // more getters/setters
}

Caution

In the example above, the table name is user. This is a reserved SQL keyword and must be quoted with backticks in Doctrine to avoid errors. You might also change the table name (e.g. with app_users) to solve this issue.

Tip

This User doesn't have a password, but you can add a password property if you also want to allow this user to login with a password (e.g. via a login form).

Your User class doesn't need to be stored in Doctrine: do whatever you need. Next, make sure you've configured a "user provider" for the user:

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

    providers:
        your_db_provider:
            entity:
                class: AppBundle:User
                property: apiKey

    # ...

That's it! Need more information about this step, see:

Step 1) Create the Authenticator Class

Suppose you have an API where your clients will send an X-AUTH-TOKEN header on each request with their API token. Your job is to read this and find the associated user (if any).

To create a custom authentication system, just create a class and make it implement AuthenticatorInterface. Or, extend the simpler AbstractGuardAuthenticator. This requires you to implement several methods:

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// src/AppBundle/Security/TokenAuthenticator.php
namespace AppBundle\Security;

use Symfony\Component\HttpFoundation\JsonResponse;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Security\Core\Authentication\Token\TokenInterface;
use Symfony\Component\Security\Core\Exception\AuthenticationException;
use Symfony\Component\Security\Core\User\UserInterface;
use Symfony\Component\Security\Core\User\UserProviderInterface;
use Symfony\Component\Security\Guard\AbstractGuardAuthenticator;

class TokenAuthenticator extends AbstractGuardAuthenticator
{
    /**
     * Called on every request to decide if this authenticator should be
     * used for the request. Returning `false` will cause this authenticator
     * to be skipped.
     */
    public function supports(Request $request)
    {
        return $request->headers->has('X-AUTH-TOKEN');
    }

    /**
     * Called on every request. Return whatever credentials you want to
     * be passed to getUser() as $credentials.
     */
    public function getCredentials(Request $request)
    {
        return $request->headers->get('X-AUTH-TOKEN');
    }

    public function getUser($credentials, UserProviderInterface $userProvider)
    {
        if (null === $credentials) {
            // The token header was empty, authentication fails with HTTP Status
            // Code 401 "Unauthorized"
            return null;
        }

        // if a User is returned, checkCredentials() is called
        return $userProvider->loadUserByUsername($credentials);
    }

    public function checkCredentials($credentials, UserInterface $user)
    {
        // check credentials - e.g. make sure the password is valid
        // no credential check is needed in this case

        // return true to cause authentication success
        return true;
    }

    public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
    {
        // on success, let the request continue
        return null;
    }

    public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
    {
        $data = [
            // you may want to customize or obfuscate the message first
            'message' => strtr($exception->getMessageKey(), $exception->getMessageData())

            // or to translate this message
            // $this->translator->trans($exception->getMessageKey(), $exception->getMessageData())
        ];

        return new JsonResponse($data, Response::HTTP_UNAUTHORIZED);
    }

    /**
     * Called when authentication is needed, but it's not sent
     */
    public function start(Request $request, AuthenticationException $authException = null)
    {
        $data = [
            // you might translate this message
            'message' => 'Authentication Required'
        ];

        return new JsonResponse($data, Response::HTTP_UNAUTHORIZED);
    }

    public function supportsRememberMe()
    {
        return false;
    }
}

3.4

AuthenticatorInterface was introduced in Symfony 3.4. In previous Symfony versions, authenticators needed to implement GuardAuthenticatorInterface.

Nice work! Each method is explained below: The Guard Authenticator Methods.

Step 2) Configure the Authenticator

To finish this, make sure your authenticator is registered as a service. If you're using the default services.yml configuration, that happens automatically.

Finally, configure your firewalls key in security.yml to use this authenticator:

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

    firewalls:
        # ...

        main:
            anonymous: ~
            logout: ~

            guard:
                authenticators:
                    - AppBundle\Security\TokenAuthenticator

            # if you want, disable storing the user in the session
            # stateless: true

            # maybe other things, like form_login, remember_me, etc
            # ...

You did it! You now have a fully-working API token authentication system. If your homepage required ROLE_USER, then you could test it under different conditions:

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# test with no token
curl http://localhost:8000/
# {"message":"Authentication Required"}

# test with a bad token
curl -H "X-AUTH-TOKEN: FAKE" http://localhost:8000/
# {"message":"Username could not be found."}

# test with a working token
curl -H "X-AUTH-TOKEN: REAL" http://localhost:8000/
# the homepage controller is executed: the page loads normally

Now, learn more about what each method does.

The Guard Authenticator Methods

Each authenticator needs the following methods:

supports(Request $request)

This is called on every request and your job is to decide if the authenticator should be used for this request (return true) or if it should be skipped (return false).

3.4

The supports() method was introduced in Symfony 3.4. In previous Symfony versions, the authenticator could be skipped returning null in the getCredentials() method.

getCredentials(Request $request)
Your job is to read the token (or whatever your "authentication" information is) from the request and return it. These credentials are passed to getUser().
getUser($credentials, UserProviderInterface $userProvider)
The $credentials argument is the value returned by getCredentials(). Your job is to return an object that implements UserInterface. If you do, then checkCredentials() will be called. If you return null (or throw an AuthenticationException) authentication will fail.
checkCredentials($credentials, UserInterface $user)
If getUser() returns a User object, this method is called. Your job is to verify if the credentials are correct. For a login form, this is where you would check that the password is correct for the user. To pass authentication, return true. If you return anything else (or throw an AuthenticationException), authentication will fail.
onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
This is called after successful authentication and your job is to either return a Response object that will be sent to the client or null to continue the request (e.g. allow the route/controller to be called like normal). Since this is an API where each request authenticates itself, you want to return null.
onAuthenticationFailure(Request $request, AuthenticationException $exception)
This is called if authentication fails. Your job is to return the Response object that should be sent to the client. The $exception will tell you what went wrong during authentication.
start(Request $request, AuthenticationException $authException = null)
This is called if the client accesses a URI/resource that requires authentication, but no authentication details were sent. Your job is to return a Response object that helps the user authenticate (e.g. a 401 response that says "token is missing!").
supportsRememberMe()
If you want to support "remember me" functionality, return true from this method. You will still need to activate remember_me under your firewall for it to work. Since this is a stateless API, you do not want to support "remember me" functionality in this example.
createAuthenticatedToken(UserInterface $user, string $providerKey)
If you are implementing the AuthenticatorInterface instead of extending the AbstractGuardAuthenticator class, you have to implement this method. It will be called after a successful authentication to create and return the token (a class implementing GuardTokenInterface) for the user, who was supplied as the first argument.

The picture below shows how Symfony calls Guard Authenticator methods:

Customizing Error Messages

When onAuthenticationFailure() is called, it is passed an AuthenticationException that describes how authentication failed via its $exception->getMessageKey() (and $exception->getMessageData()) method. The message will be different based on where authentication fails (i.e. getUser() versus checkCredentials()).

But, you can return a custom message by throwing a CustomUserMessageAuthenticationException. You can throw this from getCredentials(), getUser() or checkCredentials() to cause a failure:

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// src/AppBundle/Security/TokenAuthenticator.php
// ...

use Symfony\Component\Security\Core\Exception\CustomUserMessageAuthenticationException;

class TokenAuthenticator extends AbstractGuardAuthenticator
{
    // ...

    public function getCredentials(Request $request)
    {
        // ...

        if ($token == 'ILuvAPIs') {
            throw new CustomUserMessageAuthenticationException(
                'ILuvAPIs is not a real API key: it\'s just a silly phrase'
            );
        }

        // ...
    }

    // ...
}

In this case, since "ILuvAPIs" is a ridiculous API key, you could include an easter egg to return a custom message if someone tries this:

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curl -H "X-AUTH-TOKEN: ILuvAPIs" http://localhost:8000/
# {"message":"ILuvAPIs is not a real API key: it's just a silly phrase"}

Building a Login Form

If you're building a login form, use the AbstractFormLoginAuthenticator as your base class - it implements a few methods for you. Then, fill in the other methods just like with the TokenAuthenticator. Outside of Guard, you are still responsible for creating a route, controller and template for your login form.

Adding CSRF Protection

If you're using a Guard authenticator to build a login form and want to add CSRF protection, no problem!

First, add the _csrf_token to your login template.

Then, type-hint CsrfTokenManagerInterface in your __construct() method (or manually configure the security.csrf.token_manager service to be passed) and add the following logic:

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// src/AppBundle/Security/ExampleFormAuthenticator.php
// ...

use Symfony\Component\Security\Core\Exception\InvalidCsrfTokenException;
use Symfony\Component\Security\Csrf\CsrfToken;
use Symfony\Component\Security\Csrf\CsrfTokenManagerInterface;
use Symfony\Component\Security\Guard\Authenticator\AbstractFormLoginAuthenticator;

class ExampleFormAuthenticator extends AbstractFormLoginAuthenticator
{
    private $csrfTokenManager;

    public function __construct(CsrfTokenManagerInterface $csrfTokenManager)
    {
        $this->csrfTokenManager = $csrfTokenManager;
    }

    public function getCredentials(Request $request)
    {
        $csrfToken = $request->request->get('_csrf_token');

        if (false === $this->csrfTokenManager->isTokenValid(new CsrfToken('authenticate', $csrfToken))) {
            throw new InvalidCsrfTokenException('Invalid CSRF token.');
        }

        // ... all your normal logic
    }

    // ...
}

Avoid Authenticating the Browser on Every Request

If you create a Guard login system that's used by a browser and you're experiencing problems with your session or CSRF tokens, the cause could be bad behavior by your authenticator. When a Guard authenticator is meant to be used by a browser, you should not authenticate the user on every request. In other words, you need to make sure the supports() method only returns true when you actually need to authenticate the user. Why? Because, when supports() returns true (and authentication is ultimately successful), for security purposes, the user's session is "migrated" to a new session id.

This is an edge-case, and unless you're having session or CSRF token issues, you can ignore this. Here is an example of good and bad behavior:

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public function supports(Request $request)
{
    // GOOD behavior: only authenticate (i.e. return true) on a specific route
    return 'login_route' === $request->attributes->get('_route') && $request->isMethod('POST');

    // e.g. your login system authenticates by the user's IP address
    // BAD behavior: So, you decide to *always* return true so that
    // you can check the user's IP address on every request
    return true;
}

The problem occurs when your browser-based authenticator tries to authenticate the user on every request - like in the IP address-based example above. There are two possible fixes:

  1. If you do not need authentication to be stored in the session, set stateless: true under your firewall.
  2. Update your authenticator to avoid authentication if the user is already authenticated:
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// src/Security/MyIpAuthenticator.php
// ...

+ use Symfony\Component\Security\Core\Security;

class MyIpAuthenticator
{
+     private $security;

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

    public function supports(Request $request)
    {
+         // if there is already an authenticated user (likely due to the session)
+         // then return false and skip authentication: there is no need.
+         if ($this->security->getUser()) {
+             return false;
+         }

+         // the user is not logged in, so the authenticator should continue
+         return true;
    }
}

If you use autowiring, the Security service will automatically be passed to your authenticator.

Frequently Asked Questions

Can I have Multiple Authenticators?
Yes! But when you do, you'll need choose just one authenticator to be your "entry_point". This means you'll need to choose which authenticator's start() method should be called when an anonymous user tries to access a protected resource. For more details, see How to Use Multiple Guard Authenticators.
Can I use this with form_login?
Yes! form_login is one way to authenticate a user, so you could use it and then add one or more authenticators. Using a guard authenticator doesn't collide with other ways to authenticate.
Can I use this with FOSUserBundle?
Yes! Actually, FOSUserBundle doesn't handle security: it simply gives you a User object and some routes and controllers to help with login, registration, forgot password, etc. When you use FOSUserBundle, you typically use form_login to actually authenticate the user. You can continue doing that (see previous question) or use the User object from FOSUserBundle and create your own authenticator(s) (just like in this article).
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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