In that case, your front end is irrelevant, I would say. You can store the user data in a cookie or storage (the angular has this service already integrated), preferably cookie that you can control the validity, and whenever it is necessary to verify if the user is logged in, you send this information to the server and it does the validation.
Example: Generate a token with some login information to be verified, such as email, id, and encrypted mode name.
The basic idea is this. Store some information in cookie, whenever the user accesses the app or access some restricted area, send that cookie to the server and validate the user's authentication.