(Visual FoxPro) Get a Xero OAuth2 Access Token via PKCE

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Gets a Xero OAuth2 access token via PKCE.

For more information, see https://github.com/XeroAPI/Xero-Postman-Tutorial-PKCE-Edition

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

LOCAL loOauth2
LOCAL lnSuccess
LOCAL lcUrl
LOCAL lnNumMsWaited
LOCAL loSbJson

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

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

* For Xero OAuth2, set the listen port equal to the port used
* in the Authorized Redirect URL for the Client ID.
* For example, in this case the Authorized Redirect URL would be http://localhost:55568/
* (The final "/" char is important to include in your Authorized Redirect URL in the Xero application settings in the Xero developer portal.)
* Your app should choose a port not likely not used by any other application.
* See Xero OAuth2 for Desktop Apps for more information.
loOauth2.ListenPort = 55568

loOauth2.AuthorizationEndpoint = "https://login.xero.com/identity/connect/authorize"
loOauth2.TokenEndpoint = "https://identity.xero.com/connect/token"

* Replace this with your actual Client ID.
loOauth2.ClientId = "XERO_APP_OAUTH2_CLIENT_ID"

* To use PKCE, enable code challenge and set the code challenge method to "S256".
loOauth2.CodeChallenge = 1
loOauth2.CodeChallengeMethod = "S256"

* See https://developer.xero.com/documentation/oauth2/scopes for a complete list of scopes.
* You will need to change the scopes depending on what access is needed..
loOauth2.Scope = "openid profile email accounting.transactions accounting.attachments accounting.settings payroll.employees offline_access"

* Begin the OAuth2 three-legged flow.  This returns a URL that should be loaded in a browser.
lcUrl = loOauth2.StartAuth()
IF (loOauth2.LastMethodSuccess <> 1) THEN
    ? loOauth2.LastErrorText
    RELEASE loOauth2
    CANCEL
ENDIF

? "URL: " + lcUrl

* At this point, your application should load the URL in a browser.
* For example, 
* in C#: System.Diagnostics.Process.Start(url);
* in Java: Desktop.getDesktop().browse(new URI(url));
* in VBScript: Set wsh=WScript.CreateObject("WScript.Shell")
*              wsh.Run url
* in Xojo: ShowURL(url)  (see http://docs.xojo.com/index.php/ShowURL)
* in Dataflex: Runprogram Background "c:\Program Files\Internet Explorer\iexplore.exe" sUrl        
* in dBASE: run(false, 'rundll32 url.dll,FileProtocolHandler "' + lcUrl + '"')
* The Google account owner would interactively accept or deny the authorization request.

* Add the code to load the url in a web browser here...
* Add the code to load the url in a web browser here...
* Add the code to load the url in a web browser here...
* System.Diagnostics.Process.Start(url);

* Now wait for the authorization.
* We'll wait for a max of 60 seconds.
lnNumMsWaited = 0
DO WHILE (lnNumMsWaited < 60000) AND (loOauth2.AuthFlowState < 3)
    loOauth2.SleepMs(100)
    lnNumMsWaited = lnNumMsWaited + 100
ENDDO

* If there was no response from the browser within 30 seconds, then 
* the AuthFlowState will be equal to 1 or 2.
* 1: Waiting for Redirect. The OAuth2 background thread is waiting to receive the redirect HTTP request from the browser.
* 2: Waiting for Final Response. The OAuth2 background thread is waiting for the final access token response.
* In that case, cancel the background task started in the call to StartAuth.
IF (loOauth2.AuthFlowState < 3) THEN
    loOauth2.Cancel()
    ? "No response from the browser!"
    RELEASE loOauth2
    CANCEL
ENDIF

* Check the AuthFlowState to see if authorization was granted, denied, or if some error occurred
* The possible AuthFlowState values are:
* 3: Completed with Success. The OAuth2 flow has completed, the background thread exited, and the successful JSON response is available in AccessTokenResponse property.
* 4: Completed with Access Denied. The OAuth2 flow has completed, the background thread exited, and the error JSON is available in AccessTokenResponse property.
* 5: Failed Prior to Completion. The OAuth2 flow failed to complete, the background thread exited, and the error information is available in the FailureInfo property.
IF (loOauth2.AuthFlowState = 5) THEN
    ? "OAuth2 failed to complete."
    ? loOauth2.FailureInfo
    RELEASE loOauth2
    CANCEL
ENDIF

IF (loOauth2.AuthFlowState = 4) THEN
    ? "OAuth2 authorization was denied."
    ? loOauth2.AccessTokenResponse
    RELEASE loOauth2
    CANCEL
ENDIF

IF (loOauth2.AuthFlowState <> 3) THEN
    ? "Unexpected AuthFlowState:" + STR(loOauth2.AuthFlowState)
    RELEASE loOauth2
    CANCEL
ENDIF

* Save the full JSON access token response to a file.
* For versions of Chilkat < 10.0.0, use CreateObject('Chilkat_9_5_0.StringBuilder')
loSbJson = CreateObject('Chilkat.StringBuilder')
loSbJson.Append(loOauth2.AccessTokenResponse)
loSbJson.WriteFile("qa_data/tokens/xero-access-token.json","utf-8",0)

* The saved JSON response looks like this:

* 	{
* 	 "access_token": "...",
* 	 "token_type": "Bearer",
* 	 "expires_in": 3600,
* 	 "refresh_token": "..."
* 	}
* 
? "OAuth2 authorization granted!"
? "Access Token = " + loOauth2.AccessToken

RELEASE loOauth2
RELEASE loSbJson