There are multiple blog that shows how to use seperate login for yii2 application but in this article i will show you how to use a single login screen for all your YII2 Advanced, YII2 Basic, Application, It will also work when your domain on diffrent server or the same server.
Here are few Steps you need to follow ot achive this.
1. For Advanced Templates
Step 1 : Add this into your component inside
/path/common/config/main.php
'components' => [
'user' => [
'identityClass' => 'common\models\User',
'enableAutoLogin' => true,
'identityCookie' => ['name' => '_identity', 'httpOnly' => true],
],
'request' => [
'csrfParam' => '_csrf',
],
],

Step 2: Add Session and Request into main-local.php
/path/common/config/main-local.php
'components' => [
'session' => [
'cookieParams' => [
'path' => '/',
'domain' => ".example.com",
],
],
'user' => [
'identityCookie' => [
'name' => '_identity',
'path' => '/',
'domain' => ".example.com",
],
],
'request' => [
'csrfCookie' => [
'name' => '_csrf',
'path' => '/',
'domain' => ".example.com",
],
],
],

Note: example.com is the main domain. All other domain should be sub domain of this.
Step 3: Now Update the Same Validation Key for all the applications
/path/frontend/config/main-local.php
/path/backend/config/main-local.php
'components' => [
'request' => [
// !!! insert a secret key in the following (if it is empty) - this is required by cookie validation
'cookieValidationKey' => 'fFUeb5HDj2P-1a1FTIqya8qOE',
],
],

Note : Remove the Session and request keys from your main.php of Both frontend and backend application.
Step 4: Note Somethign that you also have and console application so update session, user,and request into the main-local.php of your console application
/path/console/config/main-local.php
'components' => [
'session' => null,
'user' => null,
'request' => null,
]

2. For Basic Templates
Additionaly If you have an basic templates installed for another project and you want to use same login for that templates. To Achive this follow the given steps
Step 1: Update You main-local.php of basic template
/path/basic-app/config/main-local.php

'components' => [
'session' => [
'cookieParams' => [
'path' => '/',
'domain' => ".example.com",
],
],
'user' => [
'identityCookie' => [
'name' => '_identity',
'path' => '/',
'domain' => ".example.com",
],
],
'request' => [
'csrfCookie' => [
'name' => '_csrf',
'path' => '/',
'domain' => ".example.com",
],
],

],

I Hope you understand well how to use a single login for all of your domain and subdomain or repository.
:) Thanks for Reading