(Objective-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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#import <CkoMailMan.h>
#import <CkoJsonObject.h>
#import <CkoOAuth2.h>
#import <CkoStringBuilder.h>

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

CkoMailMan *mailman = [[CkoMailMan alloc] init];

mailman.MailHost = @"outlook.office365.com";
mailman.MailPort = [NSNumber numberWithInt:995];
mailman.PopSsl = YES;

// 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.
CkoJsonObject *jsonToken = [[CkoJsonObject alloc] init];
BOOL success = [jsonToken LoadFile: @"qa_data/tokens/office365.json"];
if (success == NO) {
    NSLog(@"%@",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 != YES) {
    NSLog(@"%@",mailman.LastErrorText);
    return;
}

// Authenticate using XOAUTH2
success = [mailman Pop3Authenticate];
if (success != YES) {
    // 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 == YES) {

        // Refresh the OAuth2 access token, and if successful, save the new (refreshed) access token and try authenticating again.
        CkoOAuth2 *oauth2 = [[CkoOAuth2 alloc] init];

        // 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 != YES) {
            NSLog(@"%@",oauth2.LastErrorText);
            return;
        }

        NSLog(@"%@%@",@"New access token: ",oauth2.AccessToken);
        NSLog(@"%@%@",@"New refresh token: ",oauth2.RefreshToken);

        // Update the JSON with the new tokens.
        [jsonToken UpdateString: @"access_token" value: oauth2.AccessToken];
        [jsonToken UpdateString: @"refresh_token" value: oauth2.RefreshToken];

        // Save the new JSON access token response to a file.
        CkoStringBuilder *sbJson = [[CkoStringBuilder alloc] init];
        jsonToken.EmitCompact = NO;
        [jsonToken EmitSb: sbJson];
        [sbJson WriteFile: @"qa_data/tokens/office365.json" charset: @"utf-8" emitBom: NO];

        NSLog(@"%@%@",@"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 == NO) {
            NSLog(@"%@",mailman.LastErrorText);
            return;
        }

    }
    else {
        NSLog(@"%@",mailman.LastErrorText);
        return;
    }

}

// Find out how many emails are on the server..
int numEmails = [[mailman CheckMail] intValue];
if (numEmails < 0) {
    NSLog(@"%@",mailman.LastErrorText);
    return;
}

// Examine the POP3 session log:
NSLog(@"%@",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 != YES) {
    NSLog(@"%@",mailman.LastErrorText);
    return;
}

NSLog(@"%@",@"Finished.");