尝试从backpack.tf 获取OAuth 授权时如何修复“错误：(401) 未经授权”？

我正在尝试从https://backpack.tf/获得 OAuth 授权，如开发人员页面中所述：https : //backpack.tf/developer/pages/oauth_grants

这是我的代码：

Imports System.Net
Imports System.IO
Imports System.Text 

Public Class Form1   
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim client_id As String = "myclientid"
    Dim client_secret As String = "myclientsecret"


    Dim resp As String = WebRequestPOST("https://backpack.tf/oauth/access_token", client_id, client_secret)

    RichtextBox1.Text = resp
End Sub


Public Function WebRequestPOST(ByVal url As String, ByVal client_id As String, ByVal client_secret As String) As String
    Dim wrequest As HttpWebRequest = HttpWebRequest.Create(url)
    wrequest.ContentType = "application/x-www-form-urlencoded"
    wrequest.Accept = "1.0"       
    wrequest.Method = "POST"        


    Dim postData As String = "grant_type=client_credentials&client_id=" & client_id & "&client_secret=" & client_secret & "scope=read write"

    Dim postDataByte As Byte() = Encoding.UTF8.GetBytes(postData)

    Using Writer As New IO.BinaryWriter(wrequest.GetRequestStream)
        Writer.Write(postDataByte)
    End Using

    Dim wresponse As String = ""
    Try
        wresponse = New StreamReader(wrequest.GetResponse.GetResponseStream(), Encoding.Default).ReadToEnd
    Catch ex As Exception
        wresponse = ex.ToString
        Return wresponse
    End Try

    Return wresponse
End Function
End Class

它总是返回“System.Net.WebException：远程服务器返回错误：(401) 未经授权。在 System.Net.HttpWebRequest.GetResponse()”

我尝试了许多不同的方法，例如添加：

 wrequest.Headers.Add("Authorization", "myUserToken")

或者：

wrequest.Headers.Add("Authorization", "bearer myUserToken")

（如 reddit OAuth）但结果还是一样

我无法在https://backpack.tf/developer/上找到更多关于它的信息，甚至无法通过阅读 github 中所有现有机器人的代码。

使用 DotNetOpenAuth 库也无济于事