(C++) Google Sheets Refresh an Expired Access Token

Demonstrates how to refresh an expired access token. If a Google Sheets REST API call results in a 401 "unauthorized" response, then it is likely the access token expired. An application should be able to automatically refresh the access token with no user interaction and then re-try the request with the newly obtained access token.

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#include <CkJsonObject.h>
#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.

    //  It is assumed we previously obtained an OAuth2 access token.
    //  This example loads the JSON access token file
    //  saved by this example: Get Google Sheets OAuth2 Access Token

    CkJsonObject jsonToken;
    bool success = jsonToken.LoadFile("qa_data/tokens/googleSheets.json");
    if (success != true) {
        std::cout << "Failed to load googleSheets.json" << "\r\n";
        return;
    }

    //  The access token JSON looks like this:

    //  	{
    //  	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
    //  	 "token_type": "Bearer",
    //  	 "expires_in": 3600,
    //  	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
    //  	}
    // 

    CkOAuth2 oauth2;

    oauth2.put_TokenEndpoint("https://www.googleapis.com/oauth2/v4/token");

    //  Replace these with actual values.
    oauth2.put_ClientId("GOOGLE-CLIENT-ID");
    oauth2.put_ClientSecret("GOOGLE-CLIENT-SECRET");

    //  Get the "refresh_token"
    oauth2.put_RefreshToken(jsonToken.stringOf("refresh_token"));

    //  Send the HTTP POST to refresh the access token..
    success = oauth2.RefreshAccessToken();
    if (success != true) {
        std::cout << oauth2.lastErrorText() << "\r\n";
        return;
    }

    //  The response contains a new access token, but we must keep
    //  our existing refresh token for when we need to refresh again in the future.
    jsonToken.UpdateString("access_token",oauth2.accessToken());

    //  Save the new JSON access token response to a file.
    CkStringBuilder sbJson;
    jsonToken.put_EmitCompact(false);
    jsonToken.EmitSb(sbJson);
    sbJson.WriteFile("qa_data/tokens/googleSheets.json","utf-8",false);

    std::cout << "OAuth2 authorization granted!" << "\r\n";
    std::cout << "New Access Token = " << oauth2.accessToken() << "\r\n";
    }