Although your requirements may differ, in this section we'll introduce a few packages that often come in useful.
The internet nowadays is filled with big players like Facebook and Twitter, each one has a different structure and use; but they all support a version of OAuth for user authentication. This means that many projects may require the use of OAuth for user authentication and single sign-ins.
One highly-recommended package is a port from the Kohana PHP framework (http://kohanaframework.org). It can be found at https://github.com/fuel-packages/fuel-oauth.
This package handles the authentication with third-party services such as:
Dropbox
Flickr
LinkedIn
Tumblr
Twitter
Vimeo
When using this package, you'll need to copy the configuration file to your application configuration directory. This will allow you to add your consumer key and secret for the third party systems.