(VB.NET) Refresh HMRC OAuth2 Access Token

Demonstrates how to refresh an HMRC access token.

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

' See Get HMRC Access Token 
' for sample code showing how to obtain a HMRC access token for desktop apps.

' It is assumed we previously obtained an OAuth2 access token for HMRC.

Dim jsonToken As New Chilkat.JsonObject
Dim success As Boolean = jsonToken.LoadFile("qa_data/tokens/hmrc.json")
If (success <> True) Then
    Debug.WriteLine("Failed to load hmrc.json")
    Exit Sub
End If


' The access token JSON looks something like this:

' {
'   "token_type": "Bearer",
'   "scope": "user_impersonation",
'   "expires_in": "3599",
'   "ext_expires_in": "0",
'   "expires_on": "1524783438",
'   "not_before": "1524779538",
'   "resource": "https://mydomain.api.crm.dynamics.com",
'   "access_token": "...",
'   "refresh_token": "...",
'   "id_token": "..."
' }

Dim oauth2 As New Chilkat.OAuth2

oauth2.TokenEndpoint = "https://test-api.service.hmrc.gov.uk/oauth/token"

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


' Load the access token response into the json object 
jsonToken.Load(oauth2.AccessTokenResponse)

' 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 (jsonToken.HasMember("expires_on") = False) Then
    Dim dtExpire As New Chilkat.CkDateTime
    dtExpire.SetFromCurrentSystemTime()
    dtExpire.AddSeconds(jsonToken.IntOf("expires_in"))
    jsonToken.AppendString("expires_on",dtExpire.GetAsUnixTimeStr(False))
End If


' Save the new JSON access token response to a file.
' The access + refresh tokens contained in this JSON will be needed for the next refresh.
Dim sbJson As New Chilkat.StringBuilder
jsonToken.EmitCompact = False
jsonToken.EmitSb(sbJson)
sbJson.WriteFile("qa_data/tokens/hmrc.json","utf-8",False)

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