Dropzone get signed request and upload to S3

dropzones3.js

var dz = new Dropzone('#dropzone-uploader', {
        url: '/admin/media/upload',
        acceptedFiles: 'image/jpeg',
        method: 'put',
        maxFilesize: 2,
        parallelUploads: 1,
        uploadMultiple: false,
        createImageThumbnails: false,
        autoProcessQueue: false,
        previewTemplate: $('#preview-template').html(),
        accept: function(file, done) {
            var url = $.post('/admin/media/get_s3_signed_request', {
                filePath: file.name,
                contentType: file.type,
                fileSize: file.size
            })
            .done(function(res) {
                // console.log(res);
                file.uploadURL = res.url;
                file.uploadKey = res.key;
                done();
                //
                setTimeout(function() {
                    dz.processFile(file);
                });
            })
            .fail(function(err) {
                console.log(err);
                return err;
            });
        },
        sending: function(file, xhr) {
            var _send = xhr.send;
            xhr.send = function() {
                _send.call(xhr, file);
            }
        },
        success: function(file, response){

            var req = $.post('/admin/media/save', {
                's3_path': file.uploadKey
            })
            .done(function(res) {
                var tpl = '<div class="new-image" data-id="'+res.id+'">';
                tpl += '<img src="'+res.src+'" alt="thumbnail preview" />';
                tpl += '<input type="hidden" name="images[]" value="'+res.id+'" />';
                tpl += '<span class="delete">&#215;</span>';
                tpl += '</div>';

                $('#uploaded-images').append(tpl);
            });

        },
        processing: function(file) {
            this.options.url = file.uploadURL;
        }
        
    });