// Android
if (typeof CGT != 'undefined' && typeof CGT.callback != 'undefined') {

    CGT.callback(username, password);
    CGT.close();

// iOS
} else if(registrationData.device_type === 'mobile') {
    CGT_LOGIN_CALLBACK = {
        username: username,
        password: password
    }
} else {

    ....
}