Gaping Security Hole

The other case I know of is allowing local applications to authenticate to remote services by going through browser-based authentication to get the necessary token. The local application presents an HTTP interface on localhost in order to interact with the browser, and it and the authentication site do the appropriate non-same-site handoffs, but that means the authentication site has to redirect back to the local application's HTTP interface.

It seems likely to me that the local application (as well as things like printers) ought to be able to tell the browser when linking to a remote site that the particular remote site ought to be permitted to link back.