请求标头字段在用于PHP API的AngularJS调用中不允许使用Access-Control-Allow-Origin

Question

I am using AngularJS to call php APIs but I have the following problem:

XMLHttpRequest cannot load http://www.example.com/api/v1/getCategories.php. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://example.com' is therefore not allowed access.

AngularJs code:

app.factory("Data", ['$http', 'toaster',
    function ($http, toaster) { // This service connects to our REST API

        var serviceBase = 'http://www.example.com/api/v1/';
        var conf= {headers:  {
            'Access-Control-Allow-Origin':'http://example.com',
            'Content-Type': 'application/json'
         }
        };

        var obj = {};
        obj.toast = function (data) {

            toaster.pop(data.status, "", data.message, 10000, 'trustedHtml');
        }
        obj.get = function (q) {

            return $http.get(serviceBase + q,conf).then(function (results) {

                return results.data;
            });
        };
        obj.post = function (q, object) {
              return $http.post(serviceBase + q, object, conf).then(function (results) {
                return results.data;
            });
        };
        obj.put = function (q, object) {
             return $http.put(serviceBase + q, object).then(function (results) {
                 return results.data;
            });
        };
        obj.delete = function (q) {
            return $http.delete(serviceBase + q).then(function (results) {
                return results.data;
            });
        };
        return obj;
}]);

Can you please help me to figure out what is the problem ?