totp.md

TOTP Authentication

TOTP authentication uses the TOTP algorithm to generate authentication codes. Compared to Google Authenticator two-factor provider, the TOTP two-factor provider offers more configuration options, but that means your configuration isn't necessarily compatible with the Google Authenticator app.

Several parameters can be customized:

• The number of digits (default = 6)
• The digest (default = sha1)
• The period (default = 30 seconds)
• Custom parameters can be added

ℹ️ Use the default values to configure TOTP compatible with Google Authenticator (6 digits, sha1 algorithm, 30 seconds period).

How authentication works

The user has to link their account to the TOTP first. This is done by generating a shared secret code, which is stored in the user entity. Users add the code to the TOTP app either by manually typing it in together with additional properties to configure the TOTP algorithm, or by 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 TOTP app to gain access.

Basic Configuration

To enable this authentication method add this to your configuration:

scheb_two_factor:
    totp:
        enabled: true

Your user entity has to implement Scheb\TwoFactorBundle\Model\Totp\TwoFactorInterface. To activate this method for a user, generate a secret and define the TOTP configuration. TOTP let's you configure the number of digits, the algorithm and the period of the temporary codes.

We warned, custom configurations will not be compatible with the defaults of Google Authenticator app any more. You will have to use another application (e.g. FreeOTP on Android).

<?php

namespace Acme\DemoBundle\Entity;

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

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

    // [...]

    public function isTotpAuthenticationEnabled(): bool
    {
        return $this->totpSecret ? true : false;
    }

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

    public function getTotpAuthenticationConfiguration(): TotpConfigurationInterface
    {
        // You could persist the other configuration options in the user entity to make it individual per user.
        return new TotpConfiguration($this->totpSecret, TotpConfiguration::ALGORITHM_SHA1, 20, 8);
    }
}

Configuration Options

scheb_two_factor:
    totp:
        enabled: true                  # If TOTP authentication should be enabled, default false
        server_name: Server Name       # Server name used in QR code
        issuer: Issuer Name            # Issuer name used in QR code
        window: 1                      # How many codes before/after the current one would be accepted as valid
        parameters:                    # Additional parameters added in the QR code
            image: 'https://my-service/img/logo.png'
        template: security/2fa_form.html.twig   # Template used to render the authentication form

Additional parameter

You can set additional parameters, that will be added to the provisioning URI, which is contained in the QR code. Parameters will be common for all users. Custom parameters may not be supported by all applications, but can be very interesting to customize the QR codes. In the example below, we add an image parameter with the URL to the service's logo. Some applications, such as FreeOTP, support this parameter and will associate the QR code with that logo.

scheb_two_factor:
    totp:
        parameters:
            image: 'https://my-service/img/logo.png'

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:

scheb_two_factor:
    totp:
        template: security/2fa_form.html.twig

Generating a Secret Code

The service scheb_two_factor.security.totp_authenticator provides a method to generate new secret for TOTP authentication.

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

With Symfony 4, you can use auto-wiring dependency injection to get the services:

<?php

use Scheb\TwoFactorBundle\Security\TwoFactor\Provider\Totp\TotpAuthenticatorInterface;

public function generateSecret(TotpAuthenticatorInterface $totpAuthenticatorService)
{
    $secret = $totpAuthenticatorService->generateSecret();
}

QR Codes

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

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

Use a library such as endroid/qr-code-bundle or one of the many JavaScript libraries to render the QR code image.

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.