wx.uploadFile上传时formData丢失？

上传请求发出后，后端没有收到formData里填写的字段

const uploadTask = wx.uploadFile({
        url: cosBucketMap[tmpFile.cate],
        filePath: tmpFile.file,
        name: 'file',
        timeout,
        formData: {
          'key': tmpFile.new_name,
          'success_action_status': 200,
          'Signature': cos_config.Authorization,
          'x-cos-security-token': cos_config.XCosSecurityToken,
          'Content-Type': '',
        },
        success: function(res) {},
        fail: function(res) {},
});