angular_http_interceptor.ts

@Injectable()
export class AuthInterceptor implements HttpInterceptor {

    intercept(req: HttpRequest<any>,
              next: HttpHandler): Observable<HttpEvent<any>> {

        const idToken = localStorage.getItem("id_token");

        if (idToken) {
            const cloned = req.clone({
                headers: req.headers.set("Authorization",
                    "Bearer " + idToken)
            });

            return next.handle(cloned);
        }
        else {
            return next.handle(req);
        }
    }
}