(C#) POP3 Auto-Refresh Office365 Access Token

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Demonstrates how to automatically recover from an expired OAuth2 access token when OAuth2 authentication fails in the POP3 protocol. If the server responds with "-ERR Authentication failure: unknown user name or bad password.", then we refresh the access token and retry.

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

Chilkat.MailMan mailman = new Chilkat.MailMan();

mailman.MailHost = "outlook.office365.com";
mailman.MailPort = 995;
mailman.PopSsl = true;

// Use your O365 email address here.
mailman.PopUsername = "OFFICE365_EMAIL_ADDRESS";

// When using OAuth2 authentication, leave the password empty.
mailman.PopPassword = "";

// Load our previously obtained OAuth2 access token.
Chilkat.JsonObject jsonToken = new Chilkat.JsonObject();
bool success = jsonToken.LoadFile("qa_data/tokens/office365.json");
if (success == false) {
    Debug.WriteLine(jsonToken.LastErrorText);
    return;
}

mailman.OAuth2AccessToken = jsonToken.StringOf("access_token");

// Make the TLS connection to the outlook.office365.com POP3 server.
success = mailman.Pop3Connect();
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

// Authenticate using XOAUTH2
success = mailman.Pop3Authenticate();
if (success != true) {
    // If we're still connected to the mail server, then it means the server sent a non-success response,
    // Such as:  -ERR Authentication failure: unknown user name or bad password.
    if (mailman.IsPop3Connected == true) {

        // Refresh the OAuth2 access token, and if successful, save the new (refreshed) access token and try authenticating again.
        Chilkat.OAuth2 oauth2 = new Chilkat.OAuth2();

        // Use your actual Directory (tenant) ID instead of "112d7ed6-71bf-4eba-a866-738364321bfc"
        oauth2.TokenEndpoint = "https://login.microsoftonline.com/112d7ed6-71bf-4eba-a866-738364321bfc/oauth2/v2.0/token";

        // Replace these with your Azure App Registration's 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("New Access Token = " + oauth2.AccessToken);

        // Update the mailman with the new access token.
        mailman.OAuth2AccessToken = oauth2.AccessToken;

        // Retry the authentication.
        success = mailman.Pop3Authenticate();
        if (success == false) {
            Debug.WriteLine(mailman.LastErrorText);
            return;
        }

    }
    else {
        Debug.WriteLine(mailman.LastErrorText);
        return;
    }

}

// Find out how many emails are on the server..
int numEmails = mailman.CheckMail();
if (numEmails < 0) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

// Examine the POP3 session log:
Debug.WriteLine(mailman.Pop3SessionLog);

// The POP3 session log will look something like this:

// **** Connected to outlook.office365.com:995
// < +OK The Microsoft Exchange POP3 service is ready. [QwBIADIAUABSADEANgBDAEEAMAAwADEAMgAuAG4AYQBtAHAAcgBkADEANgAuAHAAcgBvAGQALgBvAHUAdABsAG8AbwBrAC4AYwBvAG0A]
// > AUTH XOAUTH2
// < + 
// > <base64 string in XOAUTH2 format>
// < -ERR Authentication failure: unknown user name or bad password.
// > AUTH XOAUTH2
// < + 
// > <base64 string in XOAUTH2 format>
// < +OK User successfully authenticated.
// > STAT
// < +OK 248 46637086

// End the POP3 session and close the connection to the GMail server.
success = mailman.Pop3EndSession();
if (success != true) {
    Debug.WriteLine(mailman.LastErrorText);
    return;
}

Debug.WriteLine("Finished.");