(VB.NET) Automatically Refresh Token for 401 Unauthorized

Demonstrates how to automatically refresh an access token (without user interaction) when the token expires and a 401 Unauthorized response is received.

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

Dim tokenFilePath As String = "qa_data/tokens/googleCalendar.json"

' Get our current access token.
Dim jsonToken As New Chilkat.JsonObject
Dim success As Boolean = jsonToken.LoadFile(tokenFilePath)
If (jsonToken.HasMember("access_token") = False) Then
    Debug.WriteLine("No access token found.")
    Exit Sub
End If

Dim http As New Chilkat.Http
http.AuthToken = jsonToken.StringOf("access_token")

Dim jsonResponse As String = http.QuickGetStr("https://www.googleapis.com/calendar/v3/users/me/calendarList")
If (http.LastMethodSuccess <> True) Then

    If (http.LastStatus <> 401) Then
        Debug.WriteLine(http.LastErrorText)
        Debug.WriteLine("----")
        Debug.WriteLine(http.LastResponseBody)
        Exit Sub
    End If


    ' The access token must've expired. 
    ' Refresh the access token and then retry the request.
    Dim oauth2 As New Chilkat.OAuth2

    oauth2.TokenEndpoint = "https://www.googleapis.com/oauth2/v4/token"

    ' Replace these with actual values.
    oauth2.ClientId = "GOOGLE-CLIENT-ID"
    oauth2.ClientSecret = "GOOGLE-CLIENT-SECRET"

    ' Get the "refresh_token"
    oauth2.RefreshToken = jsonToken.StringOf("refresh_token")

    ' Send the HTTP POST to refresh the access token..
    success = oauth2.RefreshAccessToken()
    If (success <> True) Then
        Debug.WriteLine(oauth2.LastErrorText)
        Exit Sub
    End If


    ' The response contains a new access token, but we must keep
    ' our existing refresh token for when we need to refresh again in the future.
    jsonToken.UpdateString("access_token",oauth2.AccessToken)

    ' Save the new JSON access token response to a file.
    Dim sbJson As New Chilkat.StringBuilder
    jsonToken.EmitCompact = False
    jsonToken.EmitSb(sbJson)
    sbJson.WriteFile(tokenFilePath,"utf-8",False)

    Debug.WriteLine("OAuth2 authorization granted!")
    Debug.WriteLine("New Access Token = " & oauth2.AccessToken)

    ' re-try the original request.
    http.AuthToken = oauth2.AccessToken
    jsonResponse = http.QuickGetStr("https://www.googleapis.com/calendar/v3/users/me/calendarList")
    If (http.LastMethodSuccess <> True) Then
        Debug.WriteLine(http.LastErrorText)
        Exit Sub
    End If

End If



Debug.WriteLine(jsonResponse)
Debug.WriteLine("-----------------------------")