(Xojo Plugin) 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
success = jsonToken.LoadFile("qa_data/tokens/hmrc.json")
If (success <> True) Then
    System.DebugLog("Failed to load hmrc.json")
    Return
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
    System.DebugLog(oauth2.LastErrorText)
    Return
End If

// Load the access token response into the json object 
success = 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
    success = dtExpire.SetFromCurrentSystemTime()
    success = dtExpire.AddSeconds(jsonToken.IntOf("expires_in"))
    success = 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
success = jsonToken.EmitSb(sbJson)
success = sbJson.WriteFile("qa_data/tokens/hmrc.json","utf-8",False)

System.DebugLog("OAuth2 authorization granted!")
System.DebugLog("New Access Token = " + oauth2.AccessToken)