B4X Requires Chilkat v10.1.2+

HMRC OAuth2 Access Token

See more OAuth2 Examples

Demonstrates how to get an HMRC OAuth2 access token from a desktop (installed) application or script. This example gets an HMRC MTD VAT read/write access token. B4X

Dim success As Boolean = False

'  To further clarify, see OAuth 2.0 Authorization Flow

Dim oauth2 As ChilkatOAuth2
oauth2.Initialize("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
    Log(oauth2.LastErrorText)
    Return
End If


'  Launch the default browser on the system and navigate to the url.
'  The LaunchBrowser method was added in Chilkat v10.1.2.
success = oauth2.LaunchBrowser(url)
If success = False Then
    Log(oauth2.LastErrorText)
    Return
End If


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

'  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
    Log("No response from the browser!")
    Return
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
    Log("OAuth2 failed to complete.")
    Log(oauth2.FailureInfo)
    Return
End If


If oauth2.AuthFlowState = 4 Then
    Log("OAuth2 authorization was denied.")
    Log(oauth2.AccessTokenResponse)
    Return
End If


If oauth2.AuthFlowState <> 3 Then
    Log("Unexpected AuthFlowState:" & oauth2.AuthFlowState)
    Return
End If


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

'  Get the full JSON response:
Dim json As ChilkatJsonObject
json.Initialize
json.Load(oauth2.AccessTokenResponse)
json.EmitCompact = False
Log(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 ChilkatDateTime
    dtExpire.Initialize
    dtExpire.SetFromCurrentSystemTime
    dtExpire.AddSeconds(json.IntOf("expires_in"))
    json.AppendString("expires_on", dtExpire.GetAsUnixTimeStr(False))
End If


Log(json.Emit)

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