SSO between Angular-Application and PHP on other Domain

Hello,

I have 2 Domains.
DomainA is a SPA (Angular).
DomainB is a “normal” website using PHP.

On DomainA the user logs in and browses through the site, everything is fine.
Now I want to add a link with DomainB as target.

What I try out:

DomainA:
this.auth0Service.loginWithRedirect({
authorizationParams: {
redirect_uri: DomainB
}
})

DomainB:
$auth0 = new \Auth0\SDK\Auth0([
‘domain’ => $_ENV[‘AUTH0_DOMAIN’],
‘clientId’ => $_ENV[‘AUTH0_CLIENT_ID’],
‘clientSecret’ => $_ENV[‘AUTH0_CLIENT_SECRET’],
‘cookieSecret’ => $_ENV[‘AUTH0_COOKIE_SECRET’]
]);
$auth0Sessions = $auth0->getCredentials();

The problem:
I never get credentials on the DomainB (PHP) site.
I also don’t have a “Authentication: Bearer” in the header.

How can I link to domainB without the user login again?
Please help.
I studied the documentation for days now, but I don’t find the right solution.