Identifying users of client devices for tracking user interactions with content distributed by content provider systems

1. A method comprising:

storing, by an online system, user profiles of users of the online system;

receiving, by the online system, user interactions from a browser executing on a client device of a user;

determining, by the online system, a browser identifier for uniquely identifying the browser executing on the client device;

sending, by the online system, the browser identifier for storing on the client device;

sending, by a content provider system, content for display by the browser of the client device, wherein the content includes a tracking pixel configured to cause the browser of the client device to send a request to the online system;

responsive to receiving a first request caused by the tracking pixel, sending, by the online system, a redirect request to the browser, the redirect request causing the browser to send a second request to the content provider system, the second request including the browser identifier stored in a storage area of the client device;

storing, by the content provider system, user action logs describing user interactions with content distributed by the content provider system, each user action log storing information describing a user action performed using a particular browser executing on a particular client device, a timestamp indicating a time of the user action, and a browser identifier identifying the particular browser and obtained from the particular client device;

receiving, by the online system, from the content provider system, information describing one or more user action logs, the information comprising, for each of the one or more user action logs, a browser identifier and a timestamp;

determining, by the online system, for each of the one or more user action logs, a user associated with the browser identifier of the user action log, the determining based on user interactions performed by the user with the online system using a browser associated with the browser identifier of the user action log;

sending, by the online system, for each of the one or more user action logs, a user identifier for the determined user; and

generating, by the content provider system, a report describing user interactions associated with content distributed by the content provider system, the report using the user identifiers received from the online system.

2. The method of claim 1 , wherein the content provider system sends the content to a publishing system for including in a web page sent by the publishing system to the client device.

3. The method of claim 1 , wherein the browser identifier is stored as a cookie associated with the online system on the client device.

4. The method of claim 1 , wherein the user identifier is an external user identifier, wherein the online system stores an internal user identifier associated with the user profile of each user, wherein the external user identifier is obtained by applying a hash function to the internal user identifier.

5. The method of claim 1 , wherein determining, by the online system, a user associated with the browser identifier stored in the user action log comprises:

identifying a first user for a first browser id and a first timestamp value and identifying a second user for the first browser id and a second timestamp value.

6. The method of claim 1 , wherein determining, by the online system, a user associated with the browser identifier stored in the user action log comprises:

identifying a first user for a first browser id and a first timestamp value and identifying the first user for a second browser id and a second timestamp value.

7. A method comprising:

receiving, by a content provider system, from a publishing site, a request for content for including in a web page sent by the publishing site to a browser of a client device;

responsive to receiving the request for content, sending, by the content provider system, the requested content for display by the browser of the client device, wherein the requested content includes a tracking pixel configured to cause the browser of the client device to send a first request to an online system, wherein the online system sends a redirect request to the browser responsive to receiving the first request caused by the tracking pixel, the redirect request causing the browser to send a second request to the content provider system;

receiving, by the content provider system, from the browser of the client device, the second request identifying a user action associated with the content, the second request including a browser identifier stored in a storage area of the client device, wherein the client device received the browser identifier from an online system;

storing by the content provider system, one or more user action logs, the storing comprising, responsive to receiving the request identifying the content, storing a user action log comprising information describing the user action, a timestamp associated with the user action, and the browser identifier;

sending, by the content provider system, to the online system, information describing the one or more user action logs, the information comprising, for each of the one or more user action logs, a browser identifier and a timestamp;

receiving, by the content provider system, from the online system, for each of the one or more user action logs, a user identifier associated with the browser identifier stored in the user action log; and

generating, by the content provider system, a report describing user actions, the report based on the user identifiers received from the online system.

8. The method of claim 7 , wherein the online system determines the user identifier for a user based on a likelihood of the user using the client device at the time indicated by the timestamp of the user action log.

9. The method of claim 7 , wherein web pages sent to the client device by the content provider system are restricted from accessing information stored in the storage area.

10. The method of claim 7 , wherein the browser identifier is stored on the client device as a cookie associated with the online system, wherein web pages sent to the client device by the content provider system are restricted from accessing the cookie.

11. A non-transitory computer readable storage medium, storing instructions for:

receiving, by a content provider system, from a publishing site, a request for content for including in a web page sent by the publishing site to a browser of a client device;

responsive to receiving the request for content, sending, by the content provider system, the requested content for display by the browser of the client device, wherein the requested content includes a tracking pixel configured to cause the browser of the client device to send a first request to an online system, wherein the online system sends a redirect request to the browser responsive to receiving the first request caused by the tracking pixel, the redirect request causing the browser to send a second request to the content provider system;

receiving, by the content provider system, from the browser of the client device, the second request identifying a user action associated with the content, the second request including a browser identifier stored in a storage area of the client device, wherein the client device received the browser identifier from an online system;

storing by the content provider system, one or more user action logs, the storing comprising, responsive to receiving the request identifying the content, storing a user action log comprising information describing the user action, a timestamp associated with the user action, and the browser identifier;

sending, by the content provider system, to the online system, information describing the one or more user action logs, the information comprising, for each of the one or more user action logs, a browser identifier and a timestamp;

receiving, by the content provider system, from the online system, for each of the one or more user action logs, a user identifier associated with the browser identifier stored in the user action log; and

generating, by the content provider system, a report describing user actions, the report based on the user identifiers received from the online system.

12. The non-transitory computer readable storage medium of claim 11 , wherein the online system determines the user identifier for a user based on a likelihood of the user using the client device at the time indicated by the timestamp of the user action log.

13. The non-transitory computer readable storage medium of claim 11 , wherein web pages sent to the client device by the content provider system are restricted from accessing information stored in the storage area.

14. The non-transitory computer readable storage medium of claim 11 , wherein the browser identifier is stored on the client device as a cookie associated with the online system, wherein web pages sent to the client device by the content provider system are restricted from accessing the cookie.