AuthService with promise and cache

AuthService.js

angular.service('AuthService', function($q, $http) {
  
  var authStuff, promise;
  this.login = function(credentials) {

    if (!authStuff) {
      promise = $http.post(...).then(function(response) { authStuff = response.data; });
    }

    return $q(function(resolve, reject) {
      promise.then(resolve(...)).catch(reject(...));
    });
  }
})

angular.service('AuthService', function($q, $http) {

  var authStuff;
  this.login = function(credentials) {
    var promise;
    if (!authStuff) {
      promise = $http.post(...).finally(response => authStuff = response);
    }

    return authStuff ? $q.resolve(authStuff) : promise;
  }
})

Perhaps?