FB.login() response is inconsistent

Question

Most people who are trying to login with Facebook are having no trouble, but about 5% of people who try to sign up are unable to. I believe the issue is due to some people not having certain information in the response that I get back from Facebook. Why do some people not have email and location in their response even if I have requested the email and user_location permissions?

Answer 1

I looked at your javascript and saw a couple of things you should check into:

When you initialize the javascript SDK you set cookie=false and status=false. Most examples I've seen set these to true. This might not have anything to do with the 5% exceptions you are seeing, but I don't see how it would hurt to set them to true, and it might help. Give it a try and see if it makes a difference.

The bigger issue I see is your code is assuming that the permissions are granted. You really need to check the response object in the callback to FB.login. The user might not have logged in, and they might have denied some of the permissions. You need to check the response object to see if it has an error in it.

You will need to query the permissions table (fql) or do a get to /me/permissions to know what permissions they granted. It would be nice if the FB.login callback response object told you what was granted vs. denied, but it doesn't.

Also I believe there are cases where people don't have an email registered with Facebook or a location.

To summarize: you cannot trust that you will get what you ask for, you need to check the response object and handle the exceptions gracefully, reprompting for authentication with a message indicating why you are re-prompting.

Another thing you might want to consider adding is a client-side logging tool such as log4javascript (or roll your own) that gathers more information about these exceptions. There may be a pattern for example a specific browser that is not handling things well.