Login into mutiple site using login tokens/cookies?

We are looking to implement some sort of single sign-on. Is it possible to have cross-site/multiple application login?
We are already using Firebase and this library for our authentication. We are making use of the username & password auth provider.

My current login is to save some sort of token on sign-in as a cookie on a shared domain. When you try to access one of the subsites, check and validate that token. If the token is not there/expired/invalid navigate to the single sign-on application. I see there is a method to sign-in using a custom token but I don't think that is what I am looking for.

The end goal is to have a couple of websites all sharing the same Firebase project and user details but for each to be on its own domain. Once a user has logged into one, using some sort of single sign-on, they should be able to visit any other site without needing to relogg-in.

Is this use-case currently supported by @angular/fire?

@angular/fire の認証統合と、issue に記載されている Firebase username/password および custom-token フローから始めます。共有の Firebase プロジェクトで別々のドメイン間の認証を維持できるか確認します。完了とは、文書化されたサポート対象の方法、または明確な制限を確立することです。

索引モデルが issue の本文から書いたものです。