(Objective-C) OAuth2 for a GMail using a P12 Service Account Key

See more GMail REST API Examples

Note: This example does not work for Personal Google Accounts where the email domain is @gmail.com

For more information, see https://www.chilkatsoft.com/google_workspace_setup_smtp_gmail.asp

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#import <CkoHttp.h>
#import <CkoCert.h>
#import <NSString.h>
#import <CkoMailMan.h>
#import <CkoEmail.h>

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

CkoHttp *http = [[CkoHttp alloc] init];

// --------------------------------------------------------------------------------
// For a step-by-step guide for setting up your Google Workspace service account,
// see Setup Google Workspace Account for Sending SMTP GMail from a Service Account
// --------------------------------------------------------------------------------
// Begin by loading your Google service account key (.p12)
CkoCert *cert = [[CkoCert alloc] init];
BOOL success = [cert LoadPfxFile: @"c:/someDirectory/keys/chilkat25-cbd7b42afbd8.p12" password: @"notasecret"];
if (success != YES) {
    NSLog(@"%@",cert.LastErrorText);
    return;
}

// The ISS is your service account email address ending in gserviceaccount.com.
NSString *iss = @"chilkatsvc@chilkat25.iam.gserviceaccount.com";

// The scope is always the following string:
NSString *scope = @"https://mail.google.com/";

// The sub is your company email address
NSString *oauth_sub = @"bob@yourcompany.com";

// The access token is valid for this number of seconds.
int numSec = 3600;

NSString *accessToken = [http G_SvcOauthAccessToken: iss scope: scope subEmail: oauth_sub numSec: [NSNumber numberWithInt: numSec] cert: cert];
if (http.LastMethodSuccess != YES) {
    NSLog(@"%@",http.LastErrorText);
    return;
}
else {
    NSLog(@"%@%@",@"access token: ",accessToken);
}

// The access token allows us to send unlimited emails while it's valid. Once it expires, we must obtain and use a new one.

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

// Set the properties for the GMail SMTP server:
mailman.SmtpHost = @"smtp.gmail.com";
mailman.SmtpPort = [NSNumber numberWithInt:587];
mailman.StartTLS = YES;

mailman.SmtpUsername = @"bob@yourcompany.com";
mailman.OAuth2AccessToken = accessToken;

// Create a new email object
CkoEmail *email = [[CkoEmail alloc] init];

email.Subject = @"This is a test";
email.Body = @"This is a test";
email.From = @"Bob <bob@yourcompany.com>";
success = [email AddTo: @"Recipient" emailAddress: @"recipient@example.com"];
// To add more recipients, call AddTo, AddCC, or AddBcc once per recipient.

success = [mailman SendEmail: email];
if (success != YES) {
    NSLog(@"%@",mailman.LastErrorText);
    return;
}

success = [mailman CloseSmtpConnection];
if (success != YES) {
    NSLog(@"%@",@"Connection to SMTP server not closed cleanly.");
}

NSLog(@"%@",@"Successfully sent email using Gmail with a service account key.");