I have an app, and I can write to user's walls with it, having requested the publish_stream permission when they sign in.
I've also created a page and a group, and would like my app to be able to write to those. (Specifically, I want my back-end server to post some updates to those periodically, without a user being involved.) The ability to do this seems to be implied by the descriptions of the /feed parts of those here https://developers.facebook.com/docs/reference/api/page/ and here https://developers.facebook.com/docs/reference/api/group/ . However, I can't seem to find a way to authorize the app to write to these pages. Those docs say it can be done if you have publish_streams and manage_pages. OK, but how do I grant those to my app?
In the user case, you request those permissions when the user signs in via the OAuth flow. However, the page and the group never sign-in, so there's no way for them to grant the app permission. I looked around the settings pages for the group and the page, and couldn't find anything that will let me add the app. So how do I give the app the required permissions to post to the group and the page?