What does `access-control-allow-username: *` do?

I just noticed that Replit (or something) seems to add an access-control-allow-username: * header to HTTP responses from repls. What does that header do?

I would assume (though don’t quote me) that that header could be used to limit who can access the repl. Is the header the same if you’re authed with repl auth?

I’ll maybe create a test repl and experiment with it.