If we know a keyserver, we have a cookie for it. If we use an override, we don't send that cookie, which means that from the keyserver's point of view, we're a new user. The solution is to provide an override only if we don't already know a keyserver.

Depends on D10290

Provide an override to a local keyserver when a user is logged in, click a link and check if the login screen doesn't appear.