Plan how a member area meets page caching before building it. The page cache serves its stored copy to anyone, signed in or not, and never stores what a signed-in visitor sees, so personal output on a public page needs its own handling: public pages stay cached as shells, and the few personal parts arrive as fragments.
Read Member pages and the page cache first, for the rule, how to measure it and the shell-and-fragments split. Sign-in sessions and cookies covers what the sign-in cookie is, how long it lasts, what SameSite does to visitors arriving from other sites, when to use the cookie and when a bearer token, and how to keep a member's work when a session runs out. The caching model in full, for every kind of page, is in The caching model.