(Visual Basic 6.0) Refresh Expiring OAuth2 Access Token for Azure Registered App

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' We previously obtained an access token and saved the JSON to a file using this example:
' Get OAuth2 Access Token for Azure Registered App

' This example will examine the JSON and expiration date, and if near expiration will
' refresh the access token.

Dim json As New ChilkatJsonObject
Dim success As Long
success = json.LoadFile("qa_data/tokens/_myAzureApp.json")
If (success <> 1) Then
    Debug.Print "Failed to load the access token."
    Exit Sub
End If

' The contents of the JSON look like this:
' {
'   "token_type": "Bearer",
'   "scope": "User.Read Mail.ReadWrite Mail.Send",
'   "expires_in": 3600,
'   "ext_expires_in": 0,
'   "access_token": "EwBAA8l6B...",
'   "refresh_token": "MCRMdbe6Cd...",
'   "id_token": "eyJ0eXAiOiJ...",
'   "expires_on": "1494112119"
' }

' The "expires_on" value is a Unix time.
Dim dtExpire As New CkDateTime
success = dtExpire.SetFromUnixTime(0,json.IntOf("expires_on"))

' If this date/time expires within 10 minutes of the current system time, refresh the token.
If (dtExpire.ExpiresWithin(10,"minutes") <> 1) Then
    Debug.Print "No need to refresh, the access token won't expire within the next 10 minutes."
    Exit Sub
End If

' OK, we need to refresh the access token..
Dim oauth2 As New ChilkatOAuth2

' Note: The endpoint depends on the Azure App Registration.
' See How to Choose the Correct Endpoints for your Azure App Registration
oauth2.TokenEndpoint = "https://login.microsoftonline.com/common/oauth2/v2.0/token"

' Use your client ID.
oauth2.ClientId = "CLIENT_ID"

' Get the existing refresh token.
oauth2.RefreshToken = json.StringOf("refresh_token")

' Send the HTTP POST to refresh the access token.
success = oauth2.RefreshAccessToken()
If (success = 0) Then
    Debug.Print oauth2.LastErrorText
    Exit Sub
End If

Debug.Print "OAuth2 authorization granted!"
Debug.Print "Access Token = " & oauth2.AccessToken

' Get the full JSON response:
success = json.Load(oauth2.AccessTokenResponse)
json.EmitCompact = 0

' If an "expires_on" member does not exist, then add the JSON member by
' getting the current system date/time and adding the "expires_in" seconds.
' This way we'll know when the token expires.
If (json.HasMember("expires_on") <> 1) Then
    success = dtExpire.SetFromCurrentSystemTime()
    success = dtExpire.AddSeconds(json.IntOf("expires_in"))
    success = json.AppendString("expires_on",dtExpire.GetAsUnixTimeStr(0))
End If

Debug.Print json.Emit()

' Save the new access token JSON to a file for future requests.
Dim fac As New CkFileAccess
success = fac.WriteEntireTextFile("qa_data/tokens/_myAzureApp.json",json.Emit(),"utf-8",0)