fix: add auth_https_only to env.example (#3937)

.env.example

@@ -7,9 +7,13 @@
 # They are NOT managed by the Admin UI and are not stored in the database.
 
 # === First Install Token ===
-# if set the user is required to enter this token on the /first_install page
+# If set the user is required to enter this token on the /first_install page
 # FIRST_INSTALL_TOKEN="myaccesstoken"
 
+# === Security ===
+# When enabled (recommended), auth cookies require HTTPS and SSO will reject insecure HTTP.
+AUTH_HTTPS_ONLY=true
+
 # === Logging and Development ===
 
 DEBUG=False