We have a CMS that supports multiple sites, one of our features allows our users (The site admin) to connect to the site facebook account to allow status updates, create events and upload pictures to FB from with in the CMS.

The authentication needs to occur once since each site may have multiple site admins that do not have access to the site FB user name and password. We use iframe and authenticate using $facebook->require_login() which redirects the user to the FB login and authentication pages.

All this works just fine but when the user hits "Allow" the authentication will break as it will only redirect to whatever is in the "Post-Authorize Redirect URL" field making the app obsolete for any other domain except the one in the "Post-Authorize Redirect URL"

I know other API's authentication methods like in Vimeo and YouTube will allow you to specify a NEXT parameter which is the equivalent of the "Post-Authorize Redirect URL" and it can be set at run time.

How can I make this work for multiple domain names?

Any hints on this issue will be of great help