(VB.NET UWP/WinRT) Refresh Access Token on 401 Unauthorized and Retry

Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.)

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

' This example uses a previously obtained access token having permission for the 
' scope "https://www.googleapis.com/auth/cloud-platform"

' In this example, Get Google Cloud Storage OAuth2 Access Token, 
' the service account access token was saved to a text file.  This example fetches the access token from the file..
Dim sbToken As New Chilkat.StringBuilder
Dim success As Boolean = sbToken.LoadFile("qa_data/tokens/googleCloudStorageAccessToken.txt","utf-8")
If (success = False) Then
    Debug.WriteLine("Failed to load access token.")
    Exit Sub
End If


Dim http As New Chilkat.Http

http.AuthToken = sbToken.GetAsString()

' Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
http.SetUrlVar("bucket_name","chilkat-ocean")
http.SetUrlVar("object_name","starfish.jpg")
Dim url As String = "https://www.googleapis.com/storage/v1/b/{$bucket_name}/o/{$object_name}?alt=media"

' If there is an error response, then we didn't actually download the file data,
' but instead we downloaded an error response..
Dim fileData As New Chilkat.BinData
success = Await http.DownloadBdAsync(url,fileData)
Dim responseCode As Integer = http.LastStatus
If ((success = False) And (responseCode <> 401)) Then
    Debug.WriteLine(http.LastErrorText)
    Exit Sub
End If


If (responseCode = 401) Then
    Debug.WriteLine("Received 401 Unauthorized response. Attempting to refresh the access token...")

    ' May be that the access token expired.
    ' Load our JSON key and request a new access token, then retry the original request.
    Dim fac As New Chilkat.FileAccess
    Dim jsonKey As String = fac.ReadEntireTextFile("qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json","utf-8")
    If (fac.LastMethodSuccess <> True) Then
        Debug.WriteLine(fac.LastErrorText)
        Exit Sub
    End If


    Dim gAuth As New Chilkat.AuthGoogle
    gAuth.JsonKey = jsonKey
    gAuth.Scope = "https://www.googleapis.com/auth/cloud-platform"
    gAuth.ExpireNumSeconds = 3600
    gAuth.SubEmailAddress = ""

    Dim tlsSock As New Chilkat.Socket
    success = Await tlsSock.ConnectAsync("www.googleapis.com",443,True,5000)
    If (success <> True) Then
        Debug.WriteLine(tlsSock.LastErrorText)
        Exit Sub
    End If


    success = Await gAuth.ObtainAccessTokenAsync(tlsSock)
    If (success <> True) Then
        Debug.WriteLine(gAuth.LastErrorText)
        Exit Sub
    End If


    fac.WriteEntireTextFile("qa_data/tokens/googleCloudStorageAccessToken.txt",gAuth.AccessToken,"utf-8",False)

    ' Retry the original request.
    http.AuthToken = gAuth.AccessToken
    success = Await http.DownloadBdAsync(url,fileData)
    If (success = False) Then
        Debug.WriteLine(http.LastErrorText)
        Exit Sub
    End If


End If


If (responseCode <> 200) Then
    ' Get the error response
    Dim sbErrorResponse As New Chilkat.StringBuilder
    sbErrorResponse.AppendBd(fileData,"utf-8",0,0)
    Debug.WriteLine("Error response code = " & responseCode)
    Debug.WriteLine("Error:")
    Debug.WriteLine(sbErrorResponse.GetAsString())
    Exit Sub
End If



Debug.WriteLine("Success.")

' Save the downloaded data to a file.
success = fileData.WriteFile("qa_output/starfish.jpg")