Bypass login for applications on mobile devices

1. A method comprising, using one or more processors associated with a social-networking system:

authenticating, using one or more of the processors, a user of a mobile device as being a particular user of the social-networking system;

receiving, after authenticating the user of the mobile device, a first request from the mobile device to install a software application on the mobile device for accessing social-networking data associated with the user from the social-networking system;

sending, in response to the first request, a first data to the mobile device comprising the software application and a first installation identifier (ID);

receiving a second request from the mobile device to authorize the software application to access the social-networking data associated with the user from the social-networking system, the second request comprising a second installation ID, wherein the second installation ID is based on the first installation ID;

evaluating, using one or more of the processors, the second installation ID for validity; and

sending, to the mobile device, a response to the second request in accordance with the evaluation of the validity of the second installation ID.

2. The method of claim 1 , wherein:

the second installation ID is evaluated as invalid; and

the response comprises a third request to the mobile device to authenticate the user of the mobile device.

3. The method of claim 1 , wherein:

the second installation ID is evaluated as valid; and

the response comprises an access token, wherein the access token indicates the software application has been authorized by the social-networking system.

4. The method of claim 3 , wherein the access token authorizes the software application to access social-networking data from the social-networking system.

5. The method of claim 1 , wherein evaluating the second installation ID for validity comprises determining that the second installation ID is based on the first installation ID.

6. The method of claim 1 , wherein evaluating the second installation ID for validity comprises determining that the second installation ID substantially matches the first installation ID.

7. The method of claim 1 , wherein the second installation ID comprises a timestamp, wherein the timestamp is based on the time when the first data was transmitted to the mobile device.

8. The method of claim 7 , the method further comprising:

determining, using the processor, that the timestamp is older than a threshold period of time; and

indicating, using the processor, that the second installation ID is not valid.

9. The method of claim 8 , wherein the threshold period of time is 24 hours.

10. The method of claim 7 , the method further comprising:

determining, using the processor, that the timestamp is not older than a threshold period of time; and

indicating, using the processor, that the second installation ID is valid.

11. The method of claim 10 , wherein the threshold period of time is 24 hours.

12. The method of claim 1 , wherein the first installation ID or second installation ID are encrypted.

13. The method of claim 1 , wherein the second installation ID comprises information indicating that the user of the mobile device is authenticated.

14. The method of claim 1 , further comprising:

generating, using the processor, a session in response to the first request, the session comprising the first installation ID; and

storing, using the processor, the session.

15. The method of claim 14 , further comprising:

accessing, using the processor, the first installation ID from the stored session; and

wherein evaluating the second installation ID for validity comprises determining that the second installation ID substantially matches the first installation ID from the stored session.

16. The method of claim 15 , wherein the session is an application programming interface (API) session.

17. An apparatus comprising: one or more processors associated with a social-networking system; and a memory coupled to the processors comprising instructions executable by the processors, the processors operable when executing the instructions to:

authenticate a user of a mobile device as being a particular user of the social-networking system;

receive, after authenticating the user of the mobile device, a first request from the mobile device to install a software application on the mobile device for accessing social-networking data associated with the user from the social-networking system;

send, in response to the first request, a first data to the mobile device comprising the software application and a first installation identifier (ID);

receive a second request from the mobile device to authorize the software application to access the social-networking data associated with the user from the social-networking system, the second request comprising a second installation ID, wherein the second installation ID is based on the first installation ID;

evaluate the second installation ID for validity; and

send, to the mobile device, a response to the second request in accordance with the evaluation of the validity of the second installation ID.

18. One or more computer-readable non-transitory storage media embodying software that is operable when executed by using one or more processors associated with a social-networking system to:

authenticate a user of a mobile device as being a particular user of the social-networking system;

receive, after authenticating the user of the mobile device, a first request from the mobile device to install a software application on the mobile device for accessing social-networking data associated with the user from the social-networking system;

send, in response to the first request, a first data to the mobile device comprising the software application and a first installation identifier (ID);

receive a second request from the mobile device to authorize the software application to access the social-networking data associated with the user from the social-networking system, the second request comprising a second installation ID, wherein the second installation ID is based on the first installation ID;

evaluate the second installation ID for validity; and

send, to the mobile device, a response to the second request in accordance with the evaluation of the validity of the second installation ID.