(.NET Core C#) Office365 Refresh OAuth2 Access Token for SMTP, IMAP, POP

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Demonstrates how to refresh an Office365 OAuth2 access token for use in the SMTP, IMAP, and POP3 protocols.

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// 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 Office365 SMTP/IMAP/POP3 OAuth2 Access Token

// Note: Refreshing an access token does not require user-interaction.  
// Only the act of getting the initial access token requires interactive authorization from the Office365 account owner 
// (i.e. a browser is displayed and the account owner authorizes access by the app).

// Once you have the initial access token, it can be refreshed over and over again with no limits.
// A typical strategy is to write your application to automatically refresh the access token 
// when authentication fails, and then retry the operation with the new access token.
// For example, see Auto-Refresh O365 Access Token when Sending Email

Chilkat.JsonObject jsonToken = new Chilkat.JsonObject();
bool success = jsonToken.LoadFile("qa_data/tokens/office365.json");
if (success != true) {
    Debug.WriteLine("Failed to load office365.json");
    return;
}

// The access token JSON looks like this:

// {
//   "token_type": "Bearer",
//   "scope": "IMAP.AccessAsUser.All openid POP.AccessAsUser.All profile SMTP.Send email",
//   "expires_in": 3599,
//   "ext_expires_in": 3599,
//   "access_token": "...",
//   "refresh_token": "...",
//   "id_token": "...",
//   "expires_on": "1592748507"
// }

Chilkat.OAuth2 oauth2 = new Chilkat.OAuth2();

// Update to use your token endpoint.
// In the Azure Portal, in "App registrations", go to "Endpoints" (located to the right of the "+ New registration" link.)
//    Find your endpoint for the "OAuth 2.0 token endpoint (v2)"
//    See Office365 OAuth2 Endpoints

oauth2.TokenEndpoint = "https://login.microsoftonline.com/xxxxxxxxxx-71bf-4ebe-a866-738364321bf2/oauth2/v2.0/token";

// Replace these with actual values.
oauth2.ClientId = "CLIENT_ID";
oauth2.ClientSecret = "CLIENT_SECRET";

// Get the "refresh_token"
oauth2.RefreshToken = jsonToken.StringOf("refresh_token");

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

Debug.WriteLine("New access token: " + oauth2.AccessToken);
Debug.WriteLine("New refresh token: " + oauth2.RefreshToken);

// Update the JSON with the new tokens.
jsonToken.UpdateString("access_token",oauth2.AccessToken);
jsonToken.UpdateString("refresh_token",oauth2.RefreshToken);

// Save the new JSON access token response to a file.
Chilkat.StringBuilder sbJson = new Chilkat.StringBuilder();
jsonToken.EmitCompact = false;
jsonToken.EmitSb(sbJson);
sbJson.WriteFile("qa_data/tokens/office365.json","utf-8",false);

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