步驟 1： 配置 Bucket 跨域

客戶端進行表單直傳到 OSS 時，會從瀏覽器向 OSS 發送帶有 Origin 的請求消息。OSS 對帶有 Origin 頭的請求消息會進行跨域規則（CORS）的驗證。因此需要為 Bucket 設置跨域規則以支持 Post 方法。

步驟 2：配置外網域名到小程序的上傳域名白名單中

通過 OSS 控制臺查看外網域名。

登錄微信小程序平臺，配置小程序的上傳域名白名單。

步驟 3：使用 Web 端直傳實踐方案 Demo 進行上傳測試

下載應用服務器代碼

修改 Demo 中 upload.js 的密鑰和地址。

進行上傳測試。

獲取上傳需要的簽名（signature）和加密策略（policy）

使用微信小程序上傳圖片

使用 chooseImage API 進行圖片選擇，然后調用 uploadFile 進行文件上傳

幫助文檔

upload.js

accessid= '';accesskey= '';host = '';g_dirname = ''g_object_name = ''g_object_name_type = ''now = timestamp = Date.parse(new Date()) / 1000; var policyText = {  "expiration": "2020-01-01T12:00:00.000Z", //設置該Policy的失效時間，超過這個失效時間之后，就沒有辦法通過這個policy上傳文件了  "conditions": [  ["content-length-range", 0, 1048576000] // 設置上傳文件的大小限制  ]};var policyBase64 = Base64.encode(JSON.stringify(policyText))message = policyBase64var bytes = Crypto.HMAC(Crypto.SHA1, message, accesskey, { asBytes: true }) ;var signature = Crypto.util.bytesToBase64(bytes);function check_object_radio() {  var tt = document.getElementsByName('myradio');  for (var i = 0; i < tt.length ; i++ )  {    if(tt[i].checked)    {      g_object_name_type = tt[i].value;      break;    }  }}function get_dirname(){  dir = document.getElementById("dirname").value;  if (dir != '' && dir.indexOf('/') != dir.length - 1)  {    dir = dir + '/'  }  //alert(dir)  g_dirname = dir}function random_string(len) {　　len = len || 32;　　var chars = 'ABCDEFGHJKMNPQRSTWXYZabcdefhijkmnprstwxyz2345678';  　　var maxPos = chars.length;　　var pwd = '';　　for (i = 0; i < len; i++) {  　　pwd += chars.charAt(Math.floor(Math.random() * maxPos));  }  return pwd;}function get_suffix(filename) {  pos = filename.lastIndexOf('.')  suffix = ''  if (pos != -1) {    suffix = filename.substring(pos)  }  return suffix;}function calculate_object_name(filename){  if (g_object_name_type == 'local_name')  {    g_object_name += "${filename}"  }  else if (g_object_name_type == 'random_name')  {    suffix = get_suffix(filename)    g_object_name = g_dirname + random_string(10) + suffix  }  return ''}function get_uploaded_object_name(filename){  if (g_object_name_type == 'local_name')  {    tmp_name = g_object_name    tmp_name = tmp_name.replace("${filename}", filename);    return tmp_name  }  else if(g_object_name_type == 'random_name')  {    return g_object_name  }}function set_upload_param(up, filename, ret){  g_object_name = g_dirname;  if (filename != '') {    suffix = get_suffix(filename)    calculate_object_name(filename)  }  new_multipart_params = {    'key' : g_object_name,    'policy': policyBase64,    'OSSAccessKeyId': accessid,     'success_action_status' : '200', //讓服務端返回200,不然，默認會返回204    'signature': signature,  };  up.setOption({    'url': host,    'multipart_params': new_multipart_params  });  up.start();}var uploader = new plupload.Uploader({  runtimes : 'html5,flash,silverlight,html4',  browse_button : 'selectfiles',   //multi_selection: false,  container: document.getElementById('container'),  flash_swf_url : 'lib/plupload-2.1.2/js/Moxie.swf',  silverlight_xap_url : 'lib/plupload-2.1.2/js/Moxie.xap',  url : 'http://oss.aliyuncs.com',  init: {    PostInit: function() {      document.getElementById('ossfile').innerHTML = '';      document.getElementById('postfiles').onclick = function() {      set_upload_param(uploader, '', false);      return false;      };    },    FilesAdded: function(up, files) {      plupload.each(files, function(file) {        document.getElementById('ossfile').innerHTML += '<div id="' + file.id + '">' + file.name + ' (' + plupload.formatSize(file.size) + ')<b></b>'        +'<div class="progress"><div class="progress-bar" style="width: 0%"></div></div>'        +'</div>';      });    },    BeforeUpload: function(up, file) {      check_object_radio();      get_dirname();      set_upload_param(up, file.name, true);    },    UploadProgress: function(up, file) {      var d = document.getElementById(file.id);      d.getElementsByTagName('b')[0].innerHTML = '<span>' + file.percent + "%</span>";      var prog = d.getElementsByTagName('div')[0];      var progBar = prog.getElementsByTagName('div')[0]      progBar.style.width= 2*file.percent+'px';      progBar.setAttribute('aria-valuenow', file.percent);    },    FileUploaded: function(up, file, info) {      if (info.status == 200)      {        document.getElementById(file.id).getElementsByTagName('b')[0].innerHTML = 'upload to oss success, object name:' + get_uploaded_object_name(file.name);      }      else      {        document.getElementById(file.id).getElementsByTagName('b')[0].innerHTML = info.response;      }     },    Error: function(up, err) {      document.getElementById('console').appendChild(document.createTextNode("/nError xml:" + err.response));    }  }});uploader.init();