按照https://github.com/tencentyun/wecos-ugc-upload-demo上面的操作来的

鉴权服务器应该是没有问题的，我用web试过可以成功上传文件

// upload.js

var REGION = 'ap-shanghai'

var APPID = 'xxx'

var BUCKET_NAME = 'xx'

var cosUrl = "https://" + REGION + ".file.myqcloud.com/files/v2/" + APPID + "/" + BUCKET_NAME

//填写自己的鉴权服务器地址

var cosSignatureUrl = 'xxx'

/**

* 上传方法

* filePath: 上传的文件路径

* fileName： 上传到cos后的文件名

*/

function upload(filePath, fileName) {

    // 鉴权获取签名

    wx.request({

        url: cosSignatureUrl,

        success: function (cosRes) {

            // 签名

            var signature = cosRes.data

            // 头部带上签名，上传文件至COS

            wx.uploadFile({

                url: cosUrl + '/' + fileName,

                filePath: filePath,

                header: {

                    'Authorization': signature

                },

                name: 'filecontent',

                formData: {

                    op: 'upload'

                },

                success: function (uploadRes) {

                    var data = uploadRes.data

                    console.log('uploadRes', uploadRes)

                },

                fail: function (e) {

                    console.log('e', e)

                }

            })

        }

    })

}

//index.js

sendImageMessage: function () {

    var that = this

    wx.chooseImage({

        count: 1, // 默认9

        sizeType: ['original', 'compressed'], // 可以指定是原图还是压缩图，默认二者都有

        sourceType: ['album', 'camera'], // 可以指定来源是相册还是相机，默认二者都有

        success: function (res) {

            var filePath = res.tempFilePaths[0];

            // 获取文件名

            var fileName = 'chat.jpg'

            // 文件上传cos

            uploadFn(filePath, fileName)

        },

        fail: function (res) {

            console.log("fail...")

        },

        complete: function (res) {

            console.log("完成...")

        }

    })

}