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

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// 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.

Chilkat.JsonObject json = new Chilkat.JsonObject();
bool success = json.LoadFile("qa_data/tokens/_myAzureApp.json");
if (success != true) {
    Debug.WriteLine("Failed to load the access token.");
    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.
Chilkat.CkDateTime dtExpire = new Chilkat.CkDateTime();
dtExpire.SetFromUnixTime(false,json.IntOf("expires_on"));

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

// OK, we need to refresh the access token..
Chilkat.OAuth2 oauth2 = new Chilkat.OAuth2();

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

// Use your client ID.
oauth2.ClientId = "CLIENT_ID";

// Get the existing refresh token.
oauth2.RefreshToken = json.StringOf("refresh_token");

// Send the HTTP POST to refresh the access token.
success = oauth2.RefreshAccessToken();
if (success == false) {
    Debug.WriteLine(oauth2.LastErrorText);
    return;
}

Debug.WriteLine("OAuth2 authorization granted!");
Debug.WriteLine("Access Token = " + oauth2.AccessToken);

// Get the full JSON response:
json.Load(oauth2.AccessTokenResponse);
json.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("expires_on") != true) {
    dtExpire.SetFromCurrentSystemTime();
    dtExpire.AddSeconds(json.IntOf("expires_in"));
    json.AppendString("expires_on",dtExpire.GetAsUnixTimeStr(false));
}

Debug.WriteLine(json.Emit());

// Save the new access token JSON to a file for future requests.
Chilkat.FileAccess fac = new Chilkat.FileAccess();
fac.WriteEntireTextFile("qa_data/tokens/_myAzureApp.json",json.Emit(),"utf-8",false);