Use access token for request google map track API

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VB

Hi all,

When I use X509Certificate2 for authentication Service account, i receive an access_token.
after I request "https://www.googleapis.com/tracks/v1/entities/create[^]"

appear error "The remote server returned an error: (401) Unauthorized."

My Code:

Private Sub AuthV2()
        Dim client_id As String = "XXX@developer.gserviceaccount.com"
        Dim key As String = "XXX-privatekey.p12"
        Dim client As New WebClient()
        Dim formData As New NameValueCollection()
        Dim SCOPE As String = "https://www.googleapis.com/auth/tracks"
        Dim now As Long = unix_timestamp()
        Dim exp As Long = now + 3600
        Dim jwt_header As String = "{""alg"":""RS256"",""typ"":""JWT""}"
        Dim claim As String = "{""iss"":""" & client_id & """,""scope"":""" & SCOPE & """,""aud"":""https://accounts.google.com/o/oauth2/token"",""exp"":" & exp & ",""iat"":" & now & "}"
        Dim e1 As New System.Text.ASCIIEncoding()
        Dim clearjwt As String = Base64UrlEncode(e1.GetBytes(jwt_header)) & "." & Base64UrlEncode(e1.GetBytes(claim))
        Dim buffer As Byte() = Encoding.[Default].GetBytes(clearjwt)
        Dim cert As New X509Certificate2(key, "notasecret")
        Dim cp As New CspParameters(24, "Microsoft Enhanced RSA and AES Cryptographic Provider", DirectCast(cert.PrivateKey, RSACryptoServiceProvider).CspKeyContainerInfo.KeyContainerName)
        Dim provider As New RSACryptoServiceProvider(cp)
        Dim signature As Byte()
        signature = provider.SignData(buffer, "SHA256")
        Dim assertion As String = clearjwt & "." & Base64UrlEncode(signature)
        formData("grant_type") = "assertion"
        formData("assertion_type") = "http://oauth.net/grant_type/jwt/1.0/bearer"
        formData("assertion") = assertion
        Try
            client.Headers("Content-type") = "application/x-www-form-urlencoded"
            Dim responseBytes As Byte() = client.UploadValues("https://accounts.google.com/o/oauth2/token", "POST", formData)
            Dim Result As String = Encoding.UTF8.GetString(responseBytes)
            Dim tokens As String() = Result.Split(":"c)
            For i As Integer = 0 To tokens.Length - 1
                If tokens(i).Contains("access_token") Then
                    Me.lauth_token = (tokens(i + 1).Split(","c)(0).Replace("""", ""))
                End If
            Next
        Catch ex As WebException
        End Try
        RequestGoogleAPI()
    End Sub

Private Sub RequestGoogleAPI()
        Dim request As WebRequest
        Dim postData As String
        Dim byteArray As Byte() = Nothing
        Dim dataStream As Stream
        Dim response As WebResponse
        Try
            request = WebRequest.Create("https://www.googleapis.com/tracks/v1/entities/create")
            postData = "{""entities"":[{""name"":""ABC"",""type"":""AUTOMOBILE""},{""name"":""EFG"",""type"":""AUTOMOBILE""}]}"
            byteArray = Encoding.UTF8.GetBytes(postData)
            request.ContentType = " application/json"
            request.ContentLength = byteArray.Length
            request.Timeout = 10000
            request.Method = "POST"
            'request
            dataStream = request.GetRequestStream()
            dataStream.Write(byteArray, 0, byteArray.Length)
            dataStream.Close()

            'response
            response = request.GetResponse() '' error "The remote server returned an error: (401) Unauthorized."
            dataStream = response.GetResponseStream()
        Catch ex As Exception
        End Try        
    End Sub

please help me, thank you very much!