Google Authenticator

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Google Authenticator

Google Authenticator is a popular implementation of a TOTP algorithm to generate authentication codes. Compared to the TOTP two-factor provider, the implementation has a fixed configuration, which is necessary to be compatible with the Google Authenticator app:

  • it generates 6-digit codes
  • the code changes every 30 seconds
  • It uses the sha1 hashing algorithm

If you need different settings, please use the TOTP two-factor provider. Be warned that custom TOTP configurations likely won't be compatible with the Google Authenticator app.

How authentication works

The user has to link their account to the Google Authenticator app first. This is done by generating a shared secret code, which is stored in the user entity. Users add the code to the Google Authenticator app either by manually typing it in, or scanning a QR which automatically transfers the information.

On successful authentication the bundle checks if there is a secret stored in the user entity. If that's the case, it will ask for the authentication code. The user must enter the code currently shown in the Google Authenticator app to gain access.

For more information see the Google Authenticator website.

Installation

To make use of this feature, you have to install scheb/2fa-google-authenticator.

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composer require scheb/2fa-google-authenticator

Basic Configuration

To enable this authentication method add this to your configuration:

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# config/packages/scheb_2fa.yaml
scheb_two_factor:
    google:
        enabled: true

Your user entity has to implement Scheb\TwoFactorBundle\Model\Google\TwoFactorInterface. To activate Google Authenticator for a user, generate a secret code and persist it with the user entity.

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<?php

namespace Acme\Demo\Entity;

use Doctrine\ORM\Mapping as ORM;
use Scheb\TwoFactorBundle\Model\Google\TwoFactorInterface;
use Symfony\Component\Security\Core\User\UserInterface;

class User implements UserInterface, TwoFactorInterface
{
    /**
     * @ORM\Column(name="googleAuthenticatorSecret", type="string", nullable=true)
     */
    private $googleAuthenticatorSecret;

    // [...]

    public function isGoogleAuthenticatorEnabled(): bool
    {
        return null !== $this->googleAuthenticatorSecret;
    }

    public function getGoogleAuthenticatorUsername(): string
    {
        return $this->username;
    }

    public function getGoogleAuthenticatorSecret(): ?string
    {
        return $this->googleAuthenticatorSecret;
    }

    public function setGoogleAuthenticatorSecret(?string $googleAuthenticatorSecret): void
    {
        $this->googleAuthenticatorSecret = $googleAuthenticatorSecret;
    }
}

Configuration Reference

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# config/packages/scheb_2fa.yaml
scheb_two_factor:
    google:
        enabled: true                  # If Google Authenticator should be enabled, default false
        server_name: Server Name       # Server name used in QR code
        issuer: Issuer Name            # Issuer name used in QR code
        digits: 6                      # Number of digits in authentication code
        window: 1                      # How many codes before/after the current one would be accepted as valid
        template: security/2fa_form.html.twig   # Template used to render the authentication form

Custom Authentication Form Template

The bundle uses Resources/views/Authentication/form.html.twig to render the authentication form. If you want to use a different template you can simply register it in configuration:

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# config/packages/scheb_2fa.yaml
scheb_two_factor:
    google:
        template: security/2fa_form.html.twig

Custom Form Rendering

There are certain cases when it's not enough to just change the template. For example, you're using two-factor authentication on multiple firewalls and you need to render the form differently for each firewall. In such a case you can implement a form renderer to fully customize the rendering logic.

Create a class implementing Scheb\TwoFactorBundle\Security\TwoFactor\Provider\TwoFactorFormRendererInterface:

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<?php

namespace Acme\Demo\FormRenderer;

use Scheb\TwoFactorBundle\Security\TwoFactor\Provider\TwoFactorFormRendererInterface;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;

class MyFormRenderer implements TwoFactorFormRendererInterface
{
    // [...]

    public function renderForm(Request $request, array $templateVars): Response
    {
        // Customize form rendering
    }
}

Then register it as a service and update your configuration:

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# config/packages/scheb_2fa.yaml
scheb_two_factor:
    google:
        form_renderer: acme.custom_form_renderer_service

Generating a Secret Code

The service scheb_two_factor.security.google_authenticator provides a method to generate new secret for Google Authenticator. Auto-wiring of Scheb\TwoFactorBundle\Security\TwoFactor\Provider\Google\GoogleAuthenticatorInterface is also possible.

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$secret = $container->get("scheb_two_factor.security.google_authenticator")->generateSecret();

QR Codes

To generate a QR code that can be scanned by the Google Authenticator app, retrieve the QR code's content from Google Authenticator service:

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$qrCodeContent = $container->get("scheb_two_factor.security.google_authenticator")->getQRContent($user);

To render the QR code as an image, install scheb/2fa-qr-code:

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composer require scheb/2fa-qr-code

Use service scheb_two_factor.qr_code_generator to get the QR code image. Auto-wiring of Scheb\TwoFactorBundle\Security\TwoFactor\QrCode\QrCodeGenerator is also possible. You need to implement a small controller to display the image in your application.

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<?php

namespace App\Controller;

use Scheb\TwoFactorBundle\Security\TwoFactor\QrCode\QrCodeGenerator;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;

class QrCodeController extends AbstractController
{
    /**
     * @Route("/qr-code", name="qr_code")
     */
    public function displayGoogleAuthenticatorQrCode(QrCodeGenerator $qrCodeGenerator)
    {
        // $qrCode is provided by the endroid/qr-code library. See the docs how to customize the look of the QR code:
        // https://github.com/endroid/qr-code
        $qrCode = $qrCodeGenerator->getGoogleAuthenticatorQrCode($this->getUser());

        return new Response($qrCode->writeString(), 200, ['Content-Type' => 'image/png']);
    }
}

Caution

Security note: Keep the QR code content within your application. Render the image yourself. Do not pass the content to an external service, because this is exposing the secret code to that service.

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