(C++) 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

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#include <CkOAuth2.h>
#include <CkStringBuilder.h>

void ChilkatSample(void)
    {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkOAuth2 oauth2;
    bool success;

    // 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.
    oauth2.put_ListenPort(55568);

    oauth2.put_AuthorizationEndpoint("https://login.xero.com/identity/connect/authorize");
    oauth2.put_TokenEndpoint("https://identity.xero.com/connect/token");

    // Replace this with your actual Client ID.
    oauth2.put_ClientId("XERO_APP_OAUTH2_CLIENT_ID");

    // To use PKCE, enable code challenge and set the code challenge method to "S256".
    oauth2.put_CodeChallenge(true);
    oauth2.put_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..
    oauth2.put_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.
    const char *url = oauth2.startAuth();
    if (oauth2.get_LastMethodSuccess() != true) {
        std::cout << oauth2.lastErrorText() << "\r\n";
        return;
    }

    std::cout << "URL: " << url << "\r\n";

    // 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.
    int numMsWaited = 0;
    while ((numMsWaited < 60000) && (oauth2.get_AuthFlowState() < 3)) {
        oauth2.SleepMs(100);
        numMsWaited = numMsWaited + 100;
    }

    // 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 (oauth2.get_AuthFlowState() < 3) {
        oauth2.Cancel();
        std::cout << "No response from the browser!" << "\r\n";
        return;
    }

    // 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 (oauth2.get_AuthFlowState() == 5) {
        std::cout << "OAuth2 failed to complete." << "\r\n";
        std::cout << oauth2.failureInfo() << "\r\n";
        return;
    }

    if (oauth2.get_AuthFlowState() == 4) {
        std::cout << "OAuth2 authorization was denied." << "\r\n";
        std::cout << oauth2.accessTokenResponse() << "\r\n";
        return;
    }

    if (oauth2.get_AuthFlowState() != 3) {
        std::cout << "Unexpected AuthFlowState:" << oauth2.get_AuthFlowState() << "\r\n";
        return;
    }

    // Save the full JSON access token response to a file.
    CkStringBuilder sbJson;
    sbJson.Append(oauth2.accessTokenResponse());
    sbJson.WriteFile("qa_data/tokens/xero-access-token.json","utf-8",false);

    // The saved JSON response looks like this:

    // 	{
    // 	 "access_token": "...",
    // 	 "token_type": "Bearer",
    // 	 "expires_in": 3600,
    // 	 "refresh_token": "..."
    // 	}
    // 
    std::cout << "OAuth2 authorization granted!" << "\r\n";
    std::cout << "Access Token = " << oauth2.accessToken() << "\r\n";
    }