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?

Start with the @angular/fire authentication integration and the Firebase username/password and custom-token flows described in the issue. Check whether a shared Firebase project can preserve authentication across separate domains; done means establishing a documented supported path or a clear limitation.

Written by the indexing model from the issue text.