Facebook, Google, twitter, aside from all being social networks, all allow you to log in to third party websites with your account with them.
This is convenient for users as they have fewer logins to remember, and don’t have to repeatedly enter the same information every time they want to use a new web site.
It’s good for third party sites because it’s fast and easy for the users, and also because they often gain easy access to extended data about the user in the form of their social network.
It’s good for the social network because they get more information about what their users do when they’re not active on the network directly. This is valuable both to improve the network, but more significantly is valuable for ad targeting which allows them to make money.
There are some downsides though. For the user, a loss of privacy, and for the third party site, having to share the usage data with the identifying party.
There are a number of alternatives, but none have yet taken off.
Mozilla BrowserID/Persona is a recent attempt I’ve been experimenting with over the last couple of months.
The two core design decisions which differentiate it from other attempts are:
1. Use of am email address to identify users rather than a URI as users are used to thinking of themselves in terms of email addresses.
2. Designed to be natively implemented by browsers. This is good for preventing phishing and protecting privacy.
Like OpenID, it’s decentralised, allowing domain owners to vouch for users at that domain. One of the challenges that brings is in bootstrap. Most people don’t run their own domains, so for people to opt-in, they’d have to wait until their e-mail provider adds support. In order to work round this, Mozilla has set up a fallback system which verifies ownership of e-mail in the traditional way, with the intention that over time, fewer and fewer people will use this.