Custom Authentication System with Guard (API Token Example)

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

Guard authentication can be used to:

and many more. In this example, we'll build an API token authentication system, so we can learn more about Guard in detail.

Step 1) Prepare your User Class

Suppose you want to build 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).

First, make sure you've followed the main Security Guide to create your User class. Then add an apiToken property directly to your User class (the make:entity command is a good way to do this):

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

  // ...

  class User implements UserInterface
  {
      // ...

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

      // the getter and setter methods
  }

Don't forget to generate and run the migration:

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$ php bin/console make:migration
$ php bin/console doctrine:migrations:migrate

Next, configure your "user provider" to use this new apiToken property:

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

    providers:
        your_db_provider:
            entity:
                class: App\Entity\User
                property: apiToken

    # ...

Step 2) Create the Authenticator Class

To create a custom authentication system, 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/Security/TokenAuthenticator.php
namespace App\Security;

use App\Entity\User;
use Doctrine\ORM\EntityManagerInterface;
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
{
    private $em;

    public function __construct(EntityManagerInterface $em)
    {
        $this->em = $em;
    }

    /**
     * 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): bool
    {
        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): ?UserInterface
    {
        if (null === $credentials) {
            // The token header was empty, authentication fails with HTTP Status
            // Code 401 "Unauthorized"
            return null;
        }

        // The "username" in this case is the apiToken, see the key `property`
        // of `your_db_provider` in `security.yaml`.
        // If this returns a user, checkCredentials() is called next:
        return $userProvider->loadUserByUsername($credentials);
    }

    public function checkCredentials($credentials, UserInterface $user): bool
    {
        // Check credentials - e.g. make sure the password is valid.
        // In case of an API token, no credential check is needed.

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

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

    public function onAuthenticationFailure(Request $request, AuthenticationException $exception): ?Response
    {
        $data = [
            // you may want to customize or obfuscate the message first
            'message' => strtr($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): Response
    {
        $data = [
            // you might translate this message
            'message' => 'Authentication Required'
        ];

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

    public function supportsRememberMe(): bool
    {
        return false;
    }
}

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

Step 3) Configure the Authenticator

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

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

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

    firewalls:
        # ...

        main:
            anonymous: lazy
            logout: ~

            guard:
                authenticators:
                    - App\Security\TokenAuthenticator

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

            # ...

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).
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 false (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 also 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/Security/TokenAuthenticator.php
namespace App\Security;

// ...

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"}

Manually Authenticating a User

Sometimes you might want to manually authenticate a user - like after the user completes registration. To do that, use your authenticator and a service called GuardAuthenticatorHandler:

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

// ...
use App\Security\LoginFormAuthenticator;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\Security\Guard\GuardAuthenticatorHandler;

class RegistrationController extends AbstractController
{
    public function register(LoginFormAuthenticator $authenticator, GuardAuthenticatorHandler $guardHandler, Request $request): Response
    {
        // ...

        // after validating the user and saving them to the database
        // authenticate the user and use onAuthenticationSuccess on the authenticator
        return $guardHandler->authenticateUserAndHandleSuccess(
            $user,          // the User object you just created
            $request,
            $authenticator, // authenticator whose onAuthenticationSuccess you want to use
            'main'          // the name of your firewall in security.yaml
        );
    }
}

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): bool
{
    // 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 $request): bool
      {
+         // if there is already an authenticated user (likely due to the session)
+         // then return false and skip authentication: there is no need.
+         if ($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 to choose only 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 only 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) (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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