CSRF Protection

Introduction

CSRF protection typically entails setting a unique token to the user for that page request that matches the same token on the server. This prevents any person from submitting a form without the correct token. There are many online resources that teach what CSRF does and how it works but Masonite makes it really simple to use.

Getting Started

The CSRF features for Masonite are located in the CsrfProvider Service Provider and the CsrfMiddleware. If you do not wish to have CSRF protection then you can safely remove both of these.

The CsrfProvider simply loads the CSRF features into the container and the CsrfMiddleware is what actually generates the keys and checks if they are valid.

Templates

By default, all POST requests require a CSRF token. We can simply add a CSRF token in our forms by adding the {{ csrf_field }} tag to our form like so:

<form action="/dashboard" method="POST">
    {{ csrf_field }}

    <input type="text" name="first_name">
</form>

This will add a hidden field that looks like:

<input type="hidden" name="__token" value="8389hdnajs8...">

If this token is changed or manipulated, Masonite will throw an InvalidCsrfToken exception from inside the middleware.

If you attempt a POST request without the {{ csrf_field }} then you will receive a InvalidCsrfException exception. This just means you are either missing the Jinja2 tag or you are missing that route from the exempt class attribute in your middleware.

You can get also get the token that is generated. This is useful for JS frontends where you need to pass a CSRF token to the backend for an AJAX call

<p> Token: {{ csrf_token }} </p>

AJAX / Vue / Axios

For ajax calls, the best way to pass CSRF tokens is by setting the token inside a parent template inside a meta tag like this:

<meta name="csrf-token" content="{{ csrf_token }}">

And then you can fetch the token and put it wherever you need:

token = document.head.querySelector('meta[name="csrf-token"]')

You can then pass the token via the X-CSRF-TOKEN header instead of the __token input for ease of use.

Exempting Routes

Not all routes may require CSRF protection such as OAuth authentication or various webhooks. In order to exempt routes from protection we can add it to the exempt class attribute in the middleware located at app/http/middleware/CsrfMiddleware.py:

class CsrfMiddleware:
    """Verify CSRF Token Middleware
    """

    exempt = [
        '/oauth/github'
    ]

    ...

Now any POST routes that are to your-domain.com/oauth/github are not protected by CSRF and no checks will be made against this route. Use this sparingly as CSRF protection is crucial to application security but you may find that not all routes need it.

Exempting Multiple Routes

You can also use * wildcards for exempting several routes under the same prefix. For example you may find yourself needing to do this:

class CsrfMiddleware:
    """Verify CSRF Token Middleware
    """

    exempt = [
        '/api/document/reject-reason',
        '/api/document/@id/reject',
        '/api/document/@id/approve',
        '/api/document/@id/process/@user',
    ]

    ...

This can get a bit repetitive so you may specify a wildcard instead:

class CsrfMiddleware:
    """Verify CSRF Token Middleware
    """

    exempt = [
        '/api/document/*',
    ]

    ...