Google People API

The People API lets you list and manage the authenticated user's Contacts and retrieve profile information for authenticated users and their contacts.

For example, suppose that the authenticated user, Jen, has Fabian and Ranjith in her private contacts. When your app calls people.connections.list to retrieve a list of her connections, Jen is presented with a consent screen asking to give the app access to the list. If Jen consents, the app retrieves a list containing person resources for Fabian and Ranjith.

If the app needs information for a specific person, it can then call people.get, passing in a resource name, to get the person resource for that person.

The app can also manage contacts by creating new contacts using people.createContact, update existing contacts it has retrieved from people.connections.list using people.updateContact, and delete contacts using people.deleteContact.

Details can be found here.