Apollo middleware with Authorization header

apollo.auth-header.ts

networkInterface.use([{
    applyMiddleware(req, next) {
        let authToken = localStorage.getItem("authToken");
        if (authToken) {
            req.options.headers = Object.assign({},req.options.headers, {
                authorization: `Bearer ${authToken}`
            });
        }
        next();
    }
}]);