(Unicode C++) Refresh Expiring OAuth2 Access Token for Azure Registered App

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Shows how to renew an Azure App's access token using the refresh token when it's near expiration.

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#include <CkJsonObjectW.h>
#include <CkDateTimeW.h>
#include <CkOAuth2W.h>
#include <CkFileAccessW.h>

void ChilkatSample(void)
    {
    // We previously obtained an access token and saved the JSON to a file using this example:
    // Get OAuth2 Access Token for Azure Registered App

    // This example will examine the JSON and expiration date, and if near expiration will
    // refresh the access token.

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

    // The contents of the JSON look like this:
    // {
    //   "token_type": "Bearer",
    //   "scope": "User.Read Mail.ReadWrite Mail.Send",
    //   "expires_in": 3600,
    //   "ext_expires_in": 0,
    //   "access_token": "EwBAA8l6B...",
    //   "refresh_token": "MCRMdbe6Cd...",
    //   "id_token": "eyJ0eXAiOiJ...",
    //   "expires_on": "1494112119"
    // }

    // The "expires_on" value is a Unix time.
    CkDateTimeW dtExpire;
    dtExpire.SetFromUnixTime(false,json.IntOf(L"expires_on"));

    // If this date/time expires within 10 minutes of the current system time, refresh the token.
    if (dtExpire.ExpiresWithin(10,L"minutes") != true) {
        wprintf(L"No need to refresh, the access token won't expire within the next 10 minutes.\n");
        return;
    }

    // OK, we need to refresh the access token..
    CkOAuth2W oauth2;

    // Note: The endpoint depends on the Azure App Registration.
    // See How to Choose the Correct Endpoints for your Azure App Registration
    oauth2.put_TokenEndpoint(L"https://login.microsoftonline.com/common/oauth2/v2.0/token");

    // Use your client ID.
    oauth2.put_ClientId(L"CLIENT_ID");

    // Get the existing refresh token.
    oauth2.put_RefreshToken(json.stringOf(L"refresh_token"));

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

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

    // Get the full JSON response:
    json.Load(oauth2.accessTokenResponse());
    json.put_EmitCompact(false);

    // 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 (json.HasMember(L"expires_on") != true) {
        dtExpire.SetFromCurrentSystemTime();
        dtExpire.AddSeconds(json.IntOf(L"expires_in"));
        json.AppendString(L"expires_on",dtExpire.getAsUnixTimeStr(false));
    }

    wprintf(L"%s\n",json.emit());

    // Save the new access token JSON to a file for future requests.
    CkFileAccessW fac;
    fac.WriteEntireTextFile(L"qa_data/tokens/_myAzureApp.json",json.emit(),L"utf-8",false);
    }