(Unicode C++) Refresh GMail SMTP OAuth2 Access Token

Demonstrates how to refresh an access token for sending email via GMail (SMTP).

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#include <CkJsonObjectW.h>
#include <CkOAuth2W.h>
#include <CkStringBuilderW.h>

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

    // See Get GMail SMTP Access Token 
    // for sample code showing how to obtain a GMail SMTP access token for desktop apps.

    // It is assumed we previously obtained an OAuth2 access token for GMail (one with a scope for sending email).

    CkJsonObjectW jsonToken;
    bool success = jsonToken.LoadFile(L"qa_data/tokens/_gmailSmtp.json");
    if (success != true) {
        wprintf(L"Failed to load _gmailSmtp.json\n");
        return;
    }

    // The access token JSON looks something like this:

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

    CkOAuth2W oauth2;

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

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

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

    // Send the HTTP POST to refresh the access token..
    success = oauth2.RefreshAccessToken();
    if (success != true) {
        wprintf(L"%s\n",oauth2.lastErrorText());
        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(L"access_token",oauth2.accessToken());

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

    wprintf(L"OAuth2 authorization granted!\n");
    wprintf(L"New Access Token = %s\n",oauth2.accessToken());
    }