django-magic-link 0.1

Django app for managing tokenised 'magic link' logins.

Django Magic Link

Opinionated Django app for managing "magic link" logins.

WARNING

If you send a login link to the wrong person, they will gain full access to the user's account. Use with extreme caution, and do not use this package without reading the source code and ensuring that you are comfortable with it. If you have an internal security team, ask them to look at it before using it. If your clients have security sign-off on your application, ask them to look at it before using it.

/WARNING

This app is not intended for general purpose URL tokenisation; it is designed to support a single use case - so-called "magic link" logins.

There are lots of alternative apps that can support this use case, including the project from which this has been extracted - django-request-token. The reason for yet another one is to handle the real-world challenge of URL caching / pre-fetch, where intermediaries use URLs with unintended consequences.

This packages supports a very specific model:

1. User is sent a link to log them in automatically.
2. User clicks on the link, and which does a GET request to the URL.
3. User is presented with a confirmation page, but is not logged in.
4. User clicks on a button and performs a POST to the same page.
5. The POST request authenticates the user, and deactivates the token.

The advantage of this is the email clients do not support POST links, and any prefetch that attempts a POST will fail the CSRF checks.

The purpose is to ensure that someone actively, purposefully, clicked on a link to authenticate themselves. This enables instant deactivation of the token, so that it can no longer be used.

In practice, without this check, valid magic links may be requested a number of times via GET request before the intended recipient even sees the link. If you use a "max uses" restriction to lock down the link you may find this limit is hit, and the end user then finds that the link is inactive. The alternative to this is to remove the use limit and rely instead on an expiry window. This risks leaving the token active even after the user has logged in. This package is targeted at this situation.

Use

Prerequisite: Override the default templates.

This package has two HTML templates that must be overridden in your local application.

logmein.html

This is the landing page that a user sees when they click on the magic link. You can add any content you like to this page - the only requirement is that must contains a simple form with a csrf token and a submit button. This form must POST back to the link URL. The template render context includes the link which has a get_absolute_url method to simplify this:

<form method="POST" action="{{ link.get_absolute_url }}>
    {% csrf_token %}
    <button type="submit">Log me in</button>
</form>

error.html

If the link has expired, been used, or is being accessed by someone who is already logged in, then the error.html template will be rendered. The template context includes link and error.

<p>Error handling magic link {{ link }}: {{ error }}.</p>

1. Create a new login link

The first step in managing magic links is to create one. Links are bound to a user, and can have a custom expiry and post-login redirect URL.

# create a link with the default expiry and redirect
link = MagicLink.objects.create(user=user)

# create a link with a specific redirect
link = MagicLink.objects.create(user=user, redirect_to="/foo")

# create a link with a specific expiry (in seconds)
link = MagicLink.objects.create(user=user, expiry=60)

3. Send the link to the user

This package does not handle the sending on your behalf - it is your responsibility to ensure that you send the link to the correct user. If you send the link to the wrong user, they will have full access to the link user's account. YOU HAVE BEEN WARNED.

Settings

Settings are read from the environment first, then Django settings.

• MAGIC_LINK_DEFAULT_EXPIRY: the default link expiry, in seconds (defaults to 600 - 5 minutes).

• MAGIC_LINK_DEFAULT_REDIRECT: the default redirect URL (defaults to "/").