On the 9Lessons blog there's a recent tutorial showing you how to log into Instagram via OAuth with the help of their Instagram class.

The very quick registration gives you many users to your web project, we already published login with Facebook, Twitter and Google Plus now time to think about very popular photo sharing portal Instagram. This post explains you how to login with instagram Oauth API and importing user data. Create an instagram account and take a quick look at this demo thanks!

The tutorial walks you through the process of setting up an application in the Instagram service, configuring the scripts with the API key/secret and callback as well as the code for a simple login page. They've also included code to grab the user's information and "popular media" from the web service and pull that information into a local MySQL database.