Row Level Security in Postgres: a practical guide

alter table todos enable row level security;

create policy "Own todos" on todos
  for all to authenticated
  using (auth.uid() = user_id)
  with check (auth.uid() = user_id);

create policy "Anyone can read posts" on posts
  for select using (true);
create policy "Authors write posts" on posts
  for insert to authenticated with check (auth.uid() = author_id);

create policy "Team members read projects" on projects
  for select to authenticated
  using (exists (
    select 1 from memberships m
    where m.team_id = projects.team_id and m.user_id = auth.uid()
  ));