Abstract: A social networking system contains information describing users of the social network and various connections among the users. A user can access multiple external systems that communicate with the social networking system to access information about the users of the social networking system. Login status of the user account on the social networking system is maintained. If the login status of the user account on the social networking system indicates that the user is not logged in, the user is required to provide authentication information. If the login status of the user account indicates that the user is logged in, social network information is provided to the user via an external system, subject to the privacy settings of users of the social networking system. If the user logs out from an external system, the user is also logged out from the social networking system.

Abstract: An external system (such as a website) that interacts with users communicates with a social networking system to access information about the users, who may also be users of the social networking system. If a privacy setting is changed in the social networking system, and the change applies to information that has been shared with an external system, the change is enforced at the external system. For example, the external system may be notified that the information is invalid and must be deleted, or the external system may periodically request the information so that changes to the privacy settings are eventually experienced at the external systems. When an external system again needs the information, whether expired naturally or actively invalidated by the social network, the external system sends a new request for the information, which is subject to the (possibly revised) privacy settings.

Abstract: A social networking system contains information describing information about users of the social networking system and about various connections among the users. When a user of the social networking system accesses an external website, the external website may send the user a web page containing markup language with instructions to retrieve information associated with a user from a social networking system. The client device processes the annotations and sends a request for social information related to the user to a social networking system, subject perhaps to privacy settings in the social networking system. The user's browser uses the information obtained from the social networking system in response to the request to render the markup language document for display on the user's computer system. This process allows the external website to use information from the social networking system to enhance the user's experience on the external website.

Abstract: A social network contains information describing information about members of the social network and about various connections among the members. An external system that interacts with users (such as a website) communicates with the social network to access information about the members of the social network. In particular, the external system may determine whether a user is a member of the social network and then obtain information about the member and the member's connections within the social network. This allows an external system to use information from the social network to enhance a user's experience on the external system, while enforcing each member's privacy settings.