(Java) 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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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    CkMailMan mailman = new CkMailMan();

    mailman.put_MailHost("outlook.office365.com");
    mailman.put_MailPort(995);
    mailman.put_PopSsl(true);

    // Use your O365 email address here.
    mailman.put_PopUsername("OFFICE365_EMAIL_ADDRESS");

    // When using OAuth2 authentication, leave the password empty.
    mailman.put_PopPassword("");

    // Load our previously obtained OAuth2 access token.
    CkJsonObject jsonToken = new CkJsonObject();
    boolean success = jsonToken.LoadFile("qa_data/tokens/office365.json");
    if (success == false) {
        System.out.println(jsonToken.lastErrorText());
        return;
        }

    mailman.put_OAuth2AccessToken(jsonToken.stringOf("access_token"));

    // Make the TLS connection to the outlook.office365.com POP3 server.
    success = mailman.Pop3Connect();
    if (success != true) {
        System.out.println(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.get_IsPop3Connected() == true) {

            // Refresh the OAuth2 access token, and if successful, save the new (refreshed) access token and try authenticating again.
            CkOAuth2 oauth2 = new CkOAuth2();

            // Use your actual Directory (tenant) ID instead of "112d7ed6-71bf-4eba-a866-738364321bfc"
            oauth2.put_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.put_ClientId("CLIENT_ID");
            oauth2.put_ClientSecret("CLIENT_SECRET");

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

            // Send the HTTP POST to refresh the access token..
            success = oauth2.RefreshAccessToken();
            if (success != true) {
                System.out.println(oauth2.lastErrorText());
                return;
                }

            System.out.println("New access token: " + oauth2.accessToken());
            System.out.println("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.
            CkStringBuilder sbJson = new CkStringBuilder();
            jsonToken.put_EmitCompact(false);
            jsonToken.EmitSb(sbJson);
            sbJson.WriteFile("qa_data/tokens/office365.json","utf-8",false);

            System.out.println("New Access Token = " + oauth2.accessToken());

            // Update the mailman with the new access token.
            mailman.put_OAuth2AccessToken(oauth2.accessToken());

            // Retry the authentication.
            success = mailman.Pop3Authenticate();
            if (success == false) {
                System.out.println(mailman.lastErrorText());
                return;
                }

            }
        else {
            System.out.println(mailman.lastErrorText());
            return;
            }

        }

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

    // Examine the POP3 session log:
    System.out.println(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) {
        System.out.println(mailman.lastErrorText());
        return;
        }

    System.out.println("Finished.");
  }
}