Twitter announced friend-finding and two-step verification for Digits, its sign-in tool for developers.

Twitter launched its new mobile app development platform called Fabric in October. It’s made up of three modular kits, including a Twitter kit, which includes Digits. Digits allows people to sign into apps using their phone number. As the company explained at the time:

It’s built on Twitter infrastructure so you don’t have to worry about managing multiple relationships with carriers and SMS interchanges. Digits is fully themeable so that it fits the user experience you’ve designed for your app. Digits won’t post anything on your user’s behalf since it isn’t tied to their social network accounts, including Twitter. And with Digits, your apps are ready for global adoption: it’s available immediately in 216 countries and in 28 languages, on iOS, Android and the web.

Digits also solves a number of issues for your users. Since Digits uses a phone number, there’s no need for users to remember complex passwords or usernames and all they have to share is a phone number to get started in your app.

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In January, Twitter launched Digits for the web, enabling developers to implement phone-based login on their mobile apps’ websites.
The latest features will make it a more attractive sign-in option since they provide added security and the ability to make an app more personally relevant to the user.

“Since every app is different, many of them need their own social graphs to provide a differentiated experience to win users over,” says Twitter engineer Eric Frohnhoefer . “While social networking services give you the full list of your users’ friends, those connections may not be up to date or relevant to the app experience you’re delivering. On the other hand, contact lists on your users’ phones have the strongest, most current connections – but it can be cumbersome to build custom code to import those lists and match the contacts to create a social graph.”

Friend-finding in Digits is the solution as far as Twitter is concerned. It enables apps to create social graphs with users’ contact lists. It will match both mutual and one-way connections so users who are already on the service will know which of their contacts are also using it. They can also be alerted when a friend joins at a later time.

As Twitter notes, you can use contacts gained from the feature to personalize content with the app. For example, you could show users what their friends have bought or “the highest level they’ve achieved to incite ‘friendly’ competition”.

“By delivering an experience fit for the individual user, you can increase the adoption of your app and retention among your user base,” says Frohnhoefer. “New users will know immediately which of the people they know best are using your app and current users can be ambassadors for the new initiates. It’s worth noting too that the social graph users create in your app with Digits will not be shared with other third-party apps, and the service is opt-in for users – it won’t interrupt the simple sign-up Digits offers.”

As far as security goes, Twitter says phone-based login is already more secure than email or social-based login, but the two-step verification just adds another layer. Once you implement the verification, your app’s users can login to Digits, and set up a code, which will be prompted on future logins and signups.

Developers can get Digits at get.fabric.io, downloading Fabric, and installing the Twitter Kit. Android documentation for the new features can be found here. iOS documentation is here.

Twitter is currently in the middle of a series of developer events, which are taking place around the world. The next one is on March 11 in New York. more on those here.