Google OAuth Token error - 400 Bad Request - vb.net

Question

I'm trying to authenticate my application using OAuth2 and using the 'installed applications' flow (get auth-code and then request token). I'm getting a 400 bad request error when requesting the token on the GetResponse() line. My code is as follows:
Public Sub New()
Dim tokenRequest As WebRequest =
WebRequest.Create("https://accounts.google.com/o/oauth2/token")
Dim requestString As String = "code=<auth-code>" _
& "&client_id=<client_id>" _
& "&client_secret=<client_secret>" _
& "&redirect_uri=http://localhost" _
& "&grant_type=authorization_code"
byteArray = StrToByteArray(System.Web.HttpUtility.UrlEncode(requestString))
tokenRequest.Credentials = CredentialCache.DefaultCredentials
tokenRequest.Method = "POST"
tokenRequest.ContentLength = byteArray.Length
tokenRequest.ContentType = "application/x-www-form-urlencoded"
Dim dataStream As Stream = tokenRequest.GetRequestStream()
dataStream.Write(byteArray, 0, byteArray.Length)
dataStream.Close()
Console.WriteLine("Getting response...")
'Get response
Try
Dim response As WebResponse = tokenRequest.GetResponse()
Console.WriteLine(CType(response, HttpWebResponse).StatusDescription)
Dim data As Stream = response.GetResponseStream
Array.Resize(byteArray, 4096)
Array.Clear(byteArray, 0, byteArray.Length)
data.Read(byteArray, 0, byteArray.Length)
response.Close()
Catch wex As WebException
Console.WriteLine("ERROR! : ")
Console.WriteLine(wex.Message)
Console.WriteLine(wex.Status)
Console.WriteLine(wex.Data)
Console.WriteLine(wex.InnerException.Message)
Console.WriteLine(wex.HelpLink)
End Try
End Sub
The specifics of the error are below:
The remote server returned an error: (400) Bad Request.
7
System.Collections.ListDictionaryInternal
System.NullReferenceException: Object reference not set to an instance of an obj
ect.
at GADownload.GoogleAnalytics..ctor() in ***.vb:line 86
at GADownload.Main1.Main(String[] args) in ****.vb:line 18
I've had a look at Google GetAccessToken : Bad Request 400 and Google GData .Net OAuthUtil.GetAccessToken 400 Bad Request but have not found a solution suited to this code. I have already checked all the solutions suggested and implemented them, but with no luck so far.

Answer 1

looks like you are not setting values for the parameters auth-code, client_id or client_secret.
you can debug these parameters with a curl command to see if this is the source of the problem. e.g.
curl -X POST -d "code=<auth-code>&client_id=<client_id>&client_secret=<client_secret>"&grant_type=authorization_code" http://localhost:8000/auth/token

Answer 2

Can you try URL encoding redirect_uri
redirect_uri=http://localhost
That is the only thing I'm seeing on your code vs. mine. Here's my code that is similar in vb and working
Dim sb As New StringBuilder
sb.Append("code=").Append(Request.QueryString("code")) _
.Append("&client_id=") _
.Append(Session.Item("ClientID")) _
.Append("&client_secret=") _
.Append(Session.Item("ClientSecret")) _
.Append("&redirect_uri=") _
.Append(HttpUtility.UrlEncode("http://localhost/1.aspx")) _
.Append("&grant_type=authorization_code")
Dim requestGoogle As HttpWebRequest =
WebRequest.Create("https://accounts.google.com/o/oauth2/token")
requestGoogle.Method = "POST"
requestGoogle.ContentType = "application/x-www-form-urlencoded"
requestGoogle.ContentLength = sb.Length
Dim byteArray As Byte() = Encoding.UTF8.GetBytes(sb.ToString)
sb.Clear()
requestGoogle.GetRequestStream.Write(byteArray, 0, byteArray.Length)
byteArray = Nothing
Dim responseGoogle As HttpWebResponse = requestGoogle.GetResponse()
If responseGoogle.StatusCode = HttpStatusCode.OK Then
Dim sr As StreamReader = _
New StreamReader(responseGoogle.GetResponseStream)
Dim s As String = sr.ReadToEnd
sr.Close()
responseGoogle.GetResponseStream.Close()
requestGoogle.GetRequestStream.Close()
'Response.Write(s)
End If