.net httpsrequest谷歌硬盘刷新令牌

我正在尝试创建一个http请求，以获取一个新的accesstoken和存储的refreshtoken，以便访问Google Drive

   Dim uri As String = "https://accounts.google.com/o/oauth2/token"

   Dim para As String = "code='" + cred.RefreshToken + "'&client_id='" + ClientCredentials.CLIENT_ID + "'&client_secret='" + ClientCredentials.CLIENT_SECRET + "'&grant_type='refresh_token'"

   Dim httpWebRequest As System.Net.HttpWebRequest = Net.WebRequest.Create(uri)
   httpWebRequest.Method = "POST"
   httpWebRequest.ContentType = "application/x-www-form-urlencoded"

   Dim requestStream As System.IO.Stream = httpWebRequest.GetRequestStream()
   Dim streamwriter As System.IO.StreamWriter = New System.IO.StreamWriter(requestStream)
   streamwriter.Write(para)
   streamwriter.Close()

   Dim httpWebResponse As System.Net.HttpWebResponse = httpWebRequest.GetResponse()

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但这返回了一个错误的请求。我错过什么了吗

您没有将凭据写入StreamWriter，它应该为

streamwriter.Write(para)

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这当然是假设它们是正确的。

很抱歉，这是一个打字错误。还有什么可以发送错误的请求（400）？