C#: Facebook auto login through own application

Edit: readability and some spelling.

You mean that you want to automatically log into Facebook, once someone log into your site?

If you're using the API, the user shouldn't even need to log in to Facebook - just get the offline_access permission. I've dealt with the Facebook API myself recently, this will solve your problem. Get the permission then just pass your access token and API Key to Facebook, it should let you have what you want without the user having to be logged in to Facebook (provided you requested relevant other permission to start with the offline_access permission!)

I suggest the author to put commas, full -stops and grammar corrections in his description