Trigger Express Routes within Angular

In my MEAN app I have Angular handling all of my client-side routes. I'm creating a login page and I have Passportsetup to work with Facebook. The problem I'm currently facing is that the get request for /auth/facebook which is triggered from a link within my Angular template when 'Login with Facebook' is clicked is handled in Express because it needs passport.authenticate like so:

app.get('/auth/facebook', passport.authenticate('facebook', { scope: 'email' }));

When clicked, Angular looks for a /auth/facebook route and because it's unable to find such a route, it falls to the catch-all/otherwise route.

If I visit /auth/facebook directly from the address bar in the browser however then this works fine. So how do I get Angular to communicate with Express so that it triggers the above route correctly?