AngularJS 'Cannot read property 'then' of undefined'
<p>I've this problem, when I click on login button, the chrome console log this:</p>

<blockquote>
  <p>angular.min.js:117 TypeError: Cannot read property 'then' of undefined
      at m.$scope.logIn (loginModuleController.js:11)</p>
</blockquote>

<p>Service:</p>

<pre><code>angular.module('loginModule')
.factory('loginService', function($http){
  return{
    login: function(username, password){
      var session;
      $http.post('../server/php/auth/auth.php', {
        username: username,
        password: password
      })
      .then(function(res){
        session = res;
      });
      return session;
    },
    isLogged: function(){
      return $http.get('../angCMS/server/php/auth.php?is_logged=true');
    },
    logOut: function(){
      return $http.get('../angCMS/server/php/auth.php?logout=true');
    }
  };
});
</code></pre>

<p>controller:</p>

<pre><code>angular.module('loginModule')
.controller('LoginCtrl', ['$scope', 'loginService', function($scope, loginService){

  $scope.auth = false;

  $scope.username;
  $scope.password;
  $scope.logIn = function(){
    loginService.login($scope.username, $scope.password).then(function(response){

    }, function(res){

    });
  };

  $scope.isLogged = function(){
    loginService.isLogged()
    .then(function(response){
      if(response){
        $scope.auth = true;
      }
    });
  };

  $scope.logOut = function(){
    loginService.logOut()
    .then(function(response){
      if(response){
        $scope.auth = false;
      }
    });
  };

}]);
</code></pre>

<p>and this is the html template:</p>

<pre><code>&lt;div class="container" ng-if="auth==false"&gt;
  &lt;div class="col-md-4 col-md-offset-4"&gt;
    &lt;div class="row"&gt;
      &lt;br/&gt;&lt;h2 align="center"&gt;Login&lt;/h2&gt;
    &lt;/div&gt;
    &lt;div class="well"&gt;
        &lt;form class="form-horizontal"&gt;
        &lt;fieldset&gt;
          &lt;div class="form-group"&gt;
                &lt;input type="text" class="form-control" placeholder="Username" ng-model="username" required&gt;
          &lt;/div&gt;
          &lt;div class="form-group"&gt;
                &lt;input type="password"  class="form-control" placeholder="Password" ng-model="password" required&gt;
          &lt;/div&gt;
          &lt;div class="form-group"&gt;
                &lt;button class="btn btn-md btn-primary btn-block" type="submit" ng-click="logIn()"&gt;Sign in&lt;/button&gt;
          &lt;/div&gt;
        &lt;/fieldset&gt;
      &lt;/div&gt;
    &lt;/form&gt;
  &lt;/div&gt;
&lt;/div&gt;
</code></pre>

<p>PHP login method:</p>

<pre><code>public function login($user, $pass){

        $user = htmlspecialchars(trim($user));
        $pass = md5(htmlspecialchars(trim($pass)));

        $res = $this-&gt;DB-&gt;prepare("SELECT * FROM `admin` WHERE username = :user");
        if(!$res-&gt;execute(Array(":user"=&gt;$user)))
            die(mysql_error());

        $row = $res-&gt;fetch(PDO::FETCH_ASSOC);

        if(!$row['password'] == $pass)
            die("Errore: password errata!");

        $_SESSION['logged'] = $row;
        array_push($session, $_SESSION['logged'], true);

        return $session;
    }
</code></pre>