Using dynamic callback URLs is necessary for situations where authentication is done on a backend server with auth requests being proxied to it by a number of web servers, not a single one. Or when multiple applications are hosted on a single Web server.
Can the callback URL be set dynamically, in the authenticate() method, similarly to the option in FacebookStrategy (see some examples in https://github.com/jaredhanson/passport-facebook/issues/2):
app.get('/login', passport.authenticate('facebook', { callbackURL:"/auth/callback", successRedirect : '...', failureRedirect : '/...' }) );
Using dynamic callback URLs is necessary for situations where authentication is done on a backend server with auth requests being proxied to it by a number of web servers, not a single one. Or when multiple applications are hosted on a single Web server.