我正在尝试上传一张图片到我的S3 bucket。我使用的是AngularJS v1.2.13。当我使用他们文档中显示的简单情况（提交带有action标签的表单）时，一切都正常。但是，如果我想用ng-click的Angular方式来做，Angular会发送一个OPTIONS请求，而不是POST请求。
下面是服务代码，它首先到服务器获取签名（我知道这部分是好的），然后尝试发布所有内容。

myServices.factory('s3', function($http) {
    var service = {};

    service.upload = function(fileName) {

        return $http(
            {
                method:"POST",
                url: "sign",
                data: { "fileName": fileName }
            }
        ).then(
            function(result) {
                // success
                //resolve the promise as the data
                var data = result.data;
                var url = "https://" + data.bucket + ".s3.amazonaws.com/";

                return $http.post(url, {
                    "key": data.key,
                    "AWSAccessKeyId": data.awsKey,
                    "acl": data.acl,
                    "policy": data.policy,
                    "signature": data.signature,
                    "Content-Type": "image/jpeg",
                    "success_action_redirect": "http://localhost:3000/s3Uploaded"
            }).then(
            function(response) {
                // success
                console.log("s3.upload, success: ");
                console.log(response);
            },
            function(response) { 
                // failed
                console.log("s3.Upload, fail: ");
                console.log(response);
            }
        );

    },
        function(response) { 
            // failed
            console.log("s3.sign, fail: ");
            console.log(response);
        }
    );
};

return service;
});

我做错了什么？