Google Data interface is now supporting open OAuth stardard, this makes accessing information in Google property much easier.
OAuth is an open protocol to allow secure API authentication in a simple and standard method from desktop and web applications.
To find out more, please visit OAuth website.
The Google Data APIs Blog also gives you information on how to start using the application.
GData ( short for Google Data API ) allows users to access information stored on most of Google products. Picasa, contacts at Gmail and Google Finance are just a few examples that you can retrieve information from and display on your website.
This simply gives some site administrators to have a second option to store the information required in Google, while they don’t have enough space to store all the information needed on a single server.
GData also supports two-way communications, which means you can update your contact list or add photos to Picasa through the API.