Identity algorithms are used to avoid the pollution of the social graph or provide easy access to potential users. In the process of opening their platforms to the outside world, SNSs embraced or build several APIs. Th e aims of these APIs are to engage more users, get more content from the web or ease the access of users and interlink their content in various sites. Th e following paragraphs of the subsection refer to such APIs and protocols that are used in most of the known SNSs or sites that provide third party social networking functionalities.
OAuth provides a method for clients to access server resources on behalf of a resource owner (such as a different client or an end-user). It also provides a process for end-users to authorise third-party access to their server resources without sharing their credentials (typically, a user-name and password pair), using user-agent redirections (http://oauth.net/). Facebook platform uses OAuth 2.0 for authentication and authorisation in desktop as well as in mobile applications.
OpenID is a protocol that provides easy sign up or sign in functionality for the users. Most of the widely known web and social networking sites use openID to provide their users with single sign in username and password. Sites like Google, Yahoo!, Facebook, MySpace (http://www.myspace.com/), flickr (http://www.fl ickr.com/), wordpress (http://wordpress.com/) and many others use it in order to allow users to enter without the discouraging registration forms and with a unique login for every service. By registering once, a user is able to access any service that supports openID with the same username-password pair that s/he used for the fi rst service. Except for the above mentioned services that act also as openID providers, there are also dedicated openID providers such as claimID (http://claimid.com/), myOpenID (http://openid.net/get-an-openid/), etc.
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