I have created a web app that authenticates users on our page and I'd like to connect it with an existing Page, but cannot find that option. I only see "Create Page" in Advanced options, but that's not really what I need.
I figured since it is possible to connect an old app with an existing Page because of the group profiles being removed, it should be possible to connect new apps with existing Pages as well. Am I wrong to assume that, or just blind and did not find that option?
Sure - this is possible.
Please read the documentation for "adding a tab application to a page" at this link :
https://developers.facebook.com/docs/reference/dialogs/add_to_page/
Essentially what you have to do is initiate a dialog so that you can choose what page you want to add your application to. A direct URL example would be this :
https://www.facebook.com/dialog/pagetab?app_id=YOUR_APP_ID
&display=popup&next=YOUR_URL
Dont forget to substitute YOUR_APP_ID for your app_id and next to some other URL (doesn't have to be related to your application - it can be simple facebook.com
javascript:app_id=prompt("Enter App ID"); window.open("https://www.facebook.com/dialog/pagetab?app_id="+app_id+"&display=popup&next=https://facebook.com");