Add an /api/authcheck and use it to toggle logout/login link on top header.

api/auth.go

@@ -15,6 +15,12 @@ import (
   . "MY/webapp/common"
 )
 
+func GetApiAuthCheck(c *fiber.Ctx) error {
+  _, err := CheckAuthed(c, false)
+  // auth failure or not authed is determined by err, with nil meaning YES AUTHED
+  return c.JSON(fiber.Map{"is_authed": err == nil})
+}
+
 func GetApiLogout(c *fiber.Ctx) error {
   err := LogoutUser(c)
   if err != nil { return IfErrNil(err, c) }