I need to obtain an access_token as an App, not as an admin or user. This is so that I can post/comment/like in a the style of "[ app name ] has commented on your post".

The problem is that when I attempt to get an access token (which I do successfully), I'm getting one that is for me (the admin) because I'm logged in when I attempt to call:

https://graph.facebook.com/oauth/authorize?client_id=[app id]&redirect_uri=[url]&scope=publish_stream,offline_access&type=user_agent&display=popup

What is the process for getting an non-expiring access token AS an app, rather than an admin?

Thanks in advance