Symfony multi domain login - symfony

Question

So, I have my symfony 4 website, using multi domain.
It's not different websites, it's one website, with different languages, so I have example.com, en.example.com, ...
If we log on example.com, it works, but it doesn't make the user logged in on en.example.com.
I tried to set the config as I've seen in framework.yml:
framework:
session:
handler_id: ~
cookie_domain: '.localhost'
name: SFSESSION
But it simply breaks the login (there's no error but it 'triggers' a fail login, and no cookie is set.
If I set 'en.localhost' as a domain, it works for that subdomain, but no others obviously.
I made a test page with that code:
<?php
$currentCookieParams = session_get_cookie_params();
$rootDomain = '.localhost';
session_set_cookie_params(
$currentCookieParams["lifetime"],
$currentCookieParams["path"],
$rootDomain,
$currentCookieParams["secure"],
$currentCookieParams["httponly"]
);
session_start();
The result is that when I access localhost, I have a php cookie (on my symfony app, a similar config leads to no cookie), but if I go to test.localhost, I have nothing.
I tried to install the apache pack ( https://symfony.com/doc/current/setup/web_server_configuration.html )
And to set
php_value session.cookie_domain ".localhost"
In the .htaccess, and it doesn't work, I login on subdomain and nowhere else; it's like the htaccess is ignored.
What am I missing ?
Thank you

Answer 1

In the end, I used the apache configuration to achieve it (on production, not on my wamp).
<VirtualHost *:80>
ServerName example.com
ServerAlias www.example.com
ServerAlias *
DocumentRoot /var/www/html/examplewebsite/public
DirectoryIndex /index.php
<Directory /var/www/html/examplewebsite/public>
AllowOverride None
Order Allow,Deny
Allow from All
php_value session.cookie_domain example.com
FallbackResource /index.php
</Directory>
# uncomment the following lines if you install assets as symlinks
# or run into problems when compiling LESS/Sass/CoffeeScript assets
# <Directory /var/www/project>
# Options FollowSymlinks
# </Directory>
# optionally disable the fallback resource for the asset directories
# which will allow Apache to return a 404 error when files are
# not found instead of passing the request to Symfony
<Directory /var/www/project/public/bundles>
FallbackResource disabled
</Directory>
ErrorLog /var/log/apache2/project_error.log
CustomLog /var/log/apache2/project_access.log combined
# optionally set the value of the environment variables used in the application
#SetEnv APP_ENV prod
#SetEnv APP_SECRET <app-secret-id>
#SetEnv DATABASE_URL "mysql://db_user:db_pass#host:3306/db_name"
</VirtualHost>
The line that matters is:
php_value session.cookie_domain example.com
Apparently:
If you don't set the cookie_domain : by default the cookie is specific to the subdomain (or without subdomain) that is in the url.
If you set : .example.com : every subdomain share the cookie, but not the domain without subdomain (example.com)
If you set example.com : the simple domain, and the subdomains all share the cookie.
I'm not 100% sure it doesn't work on my wamp, didn't try for now.