Talking to an Authentication Server
Assuming you plan to write your own auth client code, it isn't event-driven, and you don't need to validate an https certificate, I would suggest using python's built-in urllib2 to call the auth server.  This will minimize dependencies, which ought to make deployment and upgrades easier.
That being said, there are more than a few existing auth-related protocols and libraries in the world, some of which might save you some time and security worries over writing code from scratch.  For example, if you make your auth server speak OpenID, many off-the-self applications and servers (including Apache) will have auth client plugins already made for you.
I'm building my startup and I'm thinking ahead for shared use of services.
So far I want to allow people who have a user account on one app to be able to use the same user account on another app. This means I will have to build an authentication server.
I would like some opinions on how to allow an app to talk to the authentication server. Should I use curl? Should I use Python's http libs? All the code will be in Python.
All it's going to do is ask the authentication server if the person is allowed to use that app and the auth server will return a JSON user object. All authorization (roles and resources) will be app independent, so this app will not have to handle that.
Sorry if this seems a bit newbish; this is the first time I have separated authentication from the actual application.