I recently needed to create some test Facebook users, but ran into a problem when I needed to get my application’s access token. So I ended up searching a bit and experimenting, and it’s simple. Turns out all you need is your application id and secret, which is right there on your application profile page (if your the developer for it). Then you just hit the oauth/authorize endpoint of the graph API, and you get back the access token:
When You Need An Application Access Token
You need to use a Facebook application access token when you have a process that acts on behalf of the application, rather than on behalf of a particular user. This happens when you access your Facebook Insights data for your app via the graph, and also when you want to create test Facebook users for your app.