feature #4: create procedure for user

resources/functions/user/check_user.sql

@@ -0,0 +1,18 @@
+create or replace function check_user(in username text, in plain_password text, out resource json) language plpgsql as
+$$
+declare
+    _username alias for username;
+begin
+    select
+       case when count(u) = 1
+       then to_json(json_populate_record(null::user_lite, to_json(u)))  -- TODO refactor this !
+       else null end
+    into resource
+    from "user" as u
+    where u.username = lower(_username)
+      and u.password = crypt(plain_password, u.password)
+    group by u;
+end;
+$$;
+
+-- drop function if exists check_user(text, text, out json);