(Visual FoxPro) Refresh HMRC OAuth2 Access Token

Demonstrates how to refresh an HMRC access token.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

LOCAL loJsonToken
LOCAL lnSuccess
LOCAL loOauth2
LOCAL loDtExpire
LOCAL loSbJson

* 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.

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.JsonObject')
loJsonToken = CreateObject('Chilkat.JsonObject')
lnSuccess = loJsonToken.LoadFile("qa_data/tokens/hmrc.json")
IF (lnSuccess <> 1) THEN
    ? "Failed to load hmrc.json"
    RELEASE loJsonToken
    CANCEL
ENDIF

* 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": "..."
* }

* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.OAuth2')
loOauth2 = CreateObject('Chilkat.OAuth2')

loOauth2.TokenEndpoint = "https://test-api.service.hmrc.gov.uk/oauth/token"

* Replace these with actual values.
loOauth2.ClientId = "HMRC-CLIENT-ID"
loOauth2.ClientSecret = "HMRC-CLIENT-SECRET"

* Get the "refresh_token"
loOauth2.RefreshToken = loJsonToken.StringOf("refresh_token")

* Send the HTTP POST to refresh the access token..
lnSuccess = loOauth2.RefreshAccessToken()
IF (lnSuccess <> 1) THEN
    ? loOauth2.LastErrorText
    RELEASE loJsonToken
    RELEASE loOauth2
    CANCEL
ENDIF

* Load the access token response into the json object 
loJsonToken.Load(loOauth2.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 (loJsonToken.HasMember("expires_on") = 0) THEN
    * For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.CkDateTime')
    loDtExpire = CreateObject('Chilkat.CkDateTime')
    loDtExpire.SetFromCurrentSystemTime()
    loDtExpire.AddSeconds(loJsonToken.IntOf("expires_in"))
    loJsonToken.AppendString("expires_on",loDtExpire.GetAsUnixTimeStr(0))
ENDIF

* 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.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbJson = CreateObject('Chilkat.StringBuilder')
loJsonToken.EmitCompact = 0
loJsonToken.EmitSb(loSbJson)
loSbJson.WriteFile("qa_data/tokens/hmrc.json","utf-8",0)

? "OAuth2 authorization granted!"
? "New Access Token = " + loOauth2.AccessToken

RELEASE loJsonToken
RELEASE loOauth2
RELEASE loDtExpire
RELEASE loSbJson