Self Authenticating Links in Django
To T. Stone's point, end users are notorious for passing links around -- ESPECIALLY those in an intraweb environment.  Having something that authenticated the user automatically means that I can almost guarantee that you're going to have at least one person logged in as somebody else. 
There are better ways, of course, to refresh a user's session from Cookie information, so you at least have a decent idea that they're a valid user attached to a valid browser and can feel SOMEwhat safer in that they aren't likely to hand their laptops about like they might with a link, but yes... to reiterate, what you're trying to do is a VERY bad idea if your app has more than 1 user.
In my web app I would like to be able to email self-authenticating links to users. These links will contain a unique token (uuid). When they click the link the token being present in the query string will be enough to authenticate them and they won't have to enter their username and password.
What's the best way to do this?