TokenInterceptor - Async HTTP Interceptors with Angular 4

token.interceptor.ts

intercept (request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    return this.auth.getUser()
        .mergeMap((user: User) => {
            
            if (user) {
                // clone and modify the request
                request = request.clone({
                    setHeaders: {
                        Authorization: `Bearer ${user.access_token}`
                    }
                });
            }
            
            return next.handle(request);
        });
}