(VB.NET) HMRC OAuth2 Access Token

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Note: This example requires Chilkat v10.1.2 or greater.

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' To further clarify, see OAuth 2.0 Authorization Flow

Dim oauth2 As New Chilkat.OAuth2

' This should be the port in the localhost callback URL for your app.
' Important: Make sure the callback URI in your HMRC developer app 
' is exactly "http://localhost:3017/".  Don't forget the ending "/" char.
' The callback URL would look like "http://localhost:3017/" if the port number is 3017.

' IMPORTANT: Don't forget to setup your HMRC application to use the Redirect URI "http://localhost:3017/" as shown
' here: Configure Redirect URI for HMRC application
oauth2.ListenPort = 3017

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

' Replace with your actual client ID
oauth2.ClientId = "HMRC-CLIENT-ID"

' The scopes are documented in the HMRC reference documentation for each API.
' This example gets a read/write access token for the HMRC MTD VAT API.
oauth2.Scope = "read:vat write:vat"


' Begin the OAuth2 Authorization code flow.  This returns a URL that should be loaded in a browser.
Dim url As String = oauth2.StartAuth()
If (oauth2.LastMethodSuccess <> True) Then
    Debug.WriteLine(oauth2.LastErrorText)
    Exit Sub
End If


' Launch the default browser on the system and navigate to the url.
' The LaunchBrowser method was added in Chilkat v10.1.2.
Dim success As Boolean = oauth2.LaunchBrowser(url)
If (success = False) Then
    Debug.WriteLine(oauth2.LastErrorText)
    Exit Sub
End If


' Wait for the user to approve or deny authorization in the browser.
Dim numMsWaited As Integer = 0
While (numMsWaited < 90000) And (oauth2.AuthFlowState < 3)
    oauth2.SleepMs(100)
    numMsWaited = numMsWaited + 100
End While

' If the browser does not respond within the specified time, AuthFlowState will be:
' 
' 1: Waiting for Redirect – The OAuth2 background thread is waiting for the browser's redirect request.
' 2: Waiting for Final Response – The thread is awaiting the final access token response.
' In either case, cancel the background task initiated by StartAuth.

If (oauth2.AuthFlowState < 3) Then
    oauth2.Cancel()
    Debug.WriteLine("No response from the browser!")
    Exit Sub
End If


' Check AuthFlowState to determine if authorization was granted, denied, or failed:
' 
' 3: Success – OAuth2 flow completed, the background thread exited, and the successful response is in AccessTokenResponse.
' 4: Access Denied – OAuth2 flow completed, the background thread exited, and the error response is in AccessTokenResponse.
' 5: Failure – OAuth2 flow failed before completion, the background thread exited, and error details are in FailureInfo.

If (oauth2.AuthFlowState = 5) Then
    Debug.WriteLine("OAuth2 failed to complete.")
    Debug.WriteLine(oauth2.FailureInfo)
    Exit Sub
End If


If (oauth2.AuthFlowState = 4) Then
    Debug.WriteLine("OAuth2 authorization was denied.")
    Debug.WriteLine(oauth2.AccessTokenResponse)
    Exit Sub
End If


If (oauth2.AuthFlowState <> 3) Then
    Debug.WriteLine("Unexpected AuthFlowState:" & oauth2.AuthFlowState)
    Exit Sub
End If

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


' Get the full JSON response:
Dim json As New Chilkat.JsonObject
json.Load(oauth2.AccessTokenResponse)
json.EmitCompact = False
Debug.WriteLine(json.Emit())

' The JSON response looks 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": "..."
' }


' 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") <> True) Then
    Dim dtExpire As New Chilkat.CkDateTime
    dtExpire.SetFromCurrentSystemTime()
    dtExpire.AddSeconds(json.IntOf("expires_in"))
    json.AppendString("expires_on",dtExpire.GetAsUnixTimeStr(False))
End If


Debug.WriteLine(json.Emit())

' Save the JSON to a file for future requests.
Dim fac As New Chilkat.FileAccess
fac.WriteEntireTextFile("qa_data/tokens/hmrc.json",json.Emit(),"utf-8",False)