Many things aren't documented at all, but I start with authentication workflow.
+==== MODIFY USERS TABLE ====
+
+=== PHP CODE ===
+
+web/Obj/dbase_base.phh
+ function LoginDBItem -> args & body
+ function LoginDBItemFromRecord -> args & body
+
+=== SQL CODE ===
+sql/sql.d/nnn-name-patch.sql
AUTHENTICATION WORKFLOW