django-visitor-pass

Django Visitor Pass

Django app for managing temporary session-based users.

Support

This project currently supports Python 3.8+, Django 3.2+.

Background

This package has been extracted out of django-request-token as a specific use case - that of temporary site "visitors". It enables a type of ephemeral user who is neither anonymous nor authenticated, but somewhere in between - known for the duration of their session.

Motivation

We've been using django-request-token for a while, and have issued over 100,000 tokens. A recent analysis showed two main use cases - single-use "magic links" for logging people in, and a more involved case where we invite unregistered users on to the platform to perform some action - providing a reference perhaps, or collaborating on something with (registered) users. The former we have extracted out into django-magic-links - and this package addresses the latter.

What is a "visitor"?

In the standard Django model you have the concept of an AnonymousUser, and an authenticated User - someone who has logged in. We have a third, intermediate, type of user - which we have historically referred to as a "Temp User", which is someone we know of, but who has not yet registered.

The canonical example of this is leaving a reference: user A on the site invites user B to leave a reference for them. They (A) give us B's name and email, we invite them to click on a link and fill out a form. That's it. We store their name and email so that we can contact them, but it's ephemeral - we don't need it, and we don't use it. Storing this data in the User table made sense (as it has name and email fields), but it led to a lot of user_type=TEMP munging to determine who is a 'real' user on the site.

What we really want is to 'stash' this information somewhere outside of the auth system, and to enable these temp users to have restricted access to specific areas of the application, for a limited period, after which we can forget about them and clear out the data.

We call these users "visitors".

Use Case - request a reference

Fred is a registered user on the site, and would like a reference from Ginger, his dance partner.

1. Fred fills out the reference request form:

   Name: Ginger
   Email: ginger@[...].com
   Message: ...
   Scope: REFERENCE_REQUEST [hidden field]

1. We save this information, and generate a unique link which we send to Ginger, along with the message.

2. Ginger clicks on the link, at which point we recognise that this is someone we know about - a "visitor" - but who is in all other respects an AnonymousUser.

3. We stash the visitor info in the standard session object - so that even though Ginger is not authenticated, we know who she is, and more importantly we know why she's here (REFERENCE_REQUEST).

4. Ginger submits the reference - which may be a multi-step process, involving GETs and POSTs, all of which are guarded by a decorator that restricts access to visitors with the appropriate Scope (just like django-request-token).

5. At the final step we can (optionally) choose to clear the session info immediately, effectively removing all further access.

Implementation

This code has been extracted out of django-request-token and simplified. It stores the visitor data in the Visitor model, and on each successful first request (where the token is 'processed' and the session filled) we record a VisitorLog record. This includes HTTP request info (session_key, referer, client IP, user-agent). This information is for analytics only - for instance determining whether links are being shared.

The app works by adding some attributes to the request and request.user objects. The user has a boolean user.is_visitor property, and the request has a request.visitor property which is the relevant Visitor object.

This is done via two bits of middleware, VisitorRequestMiddleware and VisitSessionMiddleware.

VisitorRequestMiddleware

This middleware looks for a visitor token (uuid) on the incoming request querystring. If it finds a token, it will look up the Visitor object, add it to the request, and then set the request.user.is_visitor attribute. It sets the properties from the request, and has no interaction with the session. This happens in the second piece of middleware.

VisitorSessionMiddleware

This middleware must come after the VisitorRequestMiddleware (it will blow up if it can't access request.visitor). It has two responsibilities:

1. If the request object has a visitor object on it, then it must have been set by the request middleware on the current request - so it's a new visitor, and we immediately stash it in the request.session.

2. If request.visitor is None, then we don't have a new visitor, but there may be one already stashed in the request.session, in which case we want to add it on the to the request.

Note: splitting this in two seems over-complicated, but because we are moving values from request-into-session-into-request it's a lot simpler to run two completely separate passes.

Configuration

Django Settings

1. Add visitors to INSTALLED_APPS
2. Add visitors.middleware.VisitorRequestMiddleware to MIDDLEWARE
3. Add visitors.middleware.VisitorSessionMiddleware to MIDDLEWARE

Environment Settings

• VISITOR_SESSION_KEY: session key used to stash visitor info (default: visitor:session)

• VISITOR_SESSION_EXPIRY: session expiry in seconds (default: 0 - meaning that it will expire when the browser is closed.) This settings applies as the default for all new visitor objects, but can be overridden on a per-object basis.

• VISITOR_QUERYSTRING_KEY: querystring param used on tokenised links (default: vuid)

Usage

Once you have the package configured, you can use the user_is_visitor decorator to protect views that you want to restricted to visitors only. The decorator requires a scope kwarg, which must match the Visitor.scope value set when the Visitor object is created.

@user_is_visitor(scope="foo")
def protected_view(request):
   pass

By default the decorator will allow visitors with the correct scope only. If you want more control over the access, you can pass a callable as the bypass_func param:

# allow authenticated users as well as visitors
@user_is_visitor(scope="foo", bypass_func=lambda r: r.user.is_staff)
def allow_visitors_and_staff(request):
   pass

If you don't care about the scope (you should), you can use "*" to allow all visitors access:

@user_is_visitor(scope="*")  # see also SCOPE_ANY
def allow_all_scopes(request):
   pass

Alternatively, for more complex use cases, you can ignore the decorator and just inspect the request itself:

def complicated_rules(request):
   if request.user.is_visitor:
      pass
   elif is_national_holiday():
      pass
   elif is_sunny_day():
      pass
   else:
      raise PermissionDenied