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Row Level Security

When you need granular authorization rules, nothing beats PostgreSQL's Row Level Security (RLS).

Policies are PostgreSQL's rule engine. They are incredibly powerful and flexible, allowing you to write complex SQL rules which fit your unique business needs.

Policies#

Policies are easy to understand once you get the hang of them. Each policy is attached to a table, and the policy is executed every time a table is accessed. You can just think of them as adding a WHERE clause to every query. For example a policy like this ...

create policy "Individuals can view their own todos."
on todos for select
using ( auth.uid() = user_id );

.. would translate to this whenever a user tries to select from the todos table:

select *
from todos
where auth.uid() = todos.user_id; -- Policy is implicitly added.

Helper Functions#

Supabase provides you with a few easy functions that you can use with your policies.

auth.uid()#

Returns the ID of the user making the request.

auth.role()#

Returns the role of the user making the request. In most cases this is either authenticated or anon.

auth.email()#

Returns the email of the user making the request.

Examples#

Here are some examples to show you the power of PostgreSQL's RLS.

Allow read access#

-- 1. Create table
create table profiles (
id uuid references auth.users,
avatar_url text
);
-- 2. Enable RLS
alter table profiles
enable row level security;
-- 3. Create Policy
create policy "Public profiles are viewable by everyone."
on profiles for select using (
true
);
  1. Creates a table called profiles in the public schema (default schema).
  2. Enables Row Level Security.
  3. Creates a policy which allows all select queries to run.

Restrict updates#

-- 1. Create table
create table profiles (
id uuid references auth.users,
avatar_url text
);
-- 2. Enable RLS
alter table profiles
enable row level security;
-- 3. Create Policy
create policy "Users can update their own profiles."
on profiles for update using (
auth.uid() = id
);
  1. Creates a table called profiles in the public schema (default schema).
  2. Enables RLS.
  3. Creates a policy which allows logged in users to update their own data.

Policies with joins#

Policies can even include table joins. This example shows how you can query "external" tables to build more advanced rules.

create table teams (
id serial primary key,
name text
);
-- 2. Create many to many join
create table members (
team_id bigint references teams,
user_id uuid references auth.users
);
-- 3. Enable RLS
alter table teams
enable row level security;
-- 4. Create Policy
create policy "Team members can update team details if they belong to the team."
on teams
for update using (
auth.uid() in (
select user_id from members
where team_id = id
)
);

Note: If RLS is also enabled for members, the user must also have read (select) access to members. Otherwise the joined query will not yield any results.

Policies with security definer functions#

Policies can also make use of security definer functions. This is useful in a many-to-many relationship where you want to restrict access to the linking table. Following the teams and members example from above, this example shows how you can use the security definer function in combination with a policy to control access to the members table.

-- 1. Follow example for 'Policies with joins' above
-- 2. Enable RLS
alter table members
enable row level security
-- 3. Create security definer function
create or replace function get_teams_for_authenticated_user()
returns setof bigint
language sql
security definer
set search_path = public
stable
as $$
select team_id
from members
where user_id = auth.uid()
$$;
-- 4. Create Policy
create policy "Team members can update team members if they belong to the team."
on members
for all using (
team_id in (
select get_teams_for_authenticated_user()
)
);

Verifying email domains#

Postgres has a function right(string, n) that returns the rightmost n characters of a string. You could use this to match staff member's email domains.

-- 1. Create table
create table leaderboard (
id uuid references auth.users,
high_score bigint
);
-- 2. Enable RLS
alter table leaderboard
enable row level security;
-- 3. Create Policy
create policy "Only Blizzard staff can update leaderboard"
on leaderboard
for update using (
right(auth.email(), 13) = '@blizzard.com'
);

Time to live for rows#

Policies can also be used to implement TTL or time to live feature that you see in Instagram stories or Snapchat. In the following example, rows of stories table are available only if they have been created within the last 24 hours.

-- 1. Create table
create table if not exists stories (
id uuid not null primary key DEFAULT uuid_generate_v4(),
created_at timestamp with time zone default timezone('utc' :: text, now()) not null,
content text not null
);
-- 2. Enable RLS
alter table stories
enable row level security;
-- 3. Create Policy
create policy "Stories are live for a day"
on stories
for select using (
created_at > (current_timestamp - interval '1 day')
);

Advanced policies#

Use the full power of SQL to build extremely advanced rules.

In this example, we will create a posts and comments tables and then create a policy that depends on another policy. (In this case, the comments policy depends on the posts policy.)

create table posts (
id serial primary key,
creator_id uuid not null references auth.users(id),
title text not null,
body text not null,
publish_date date not null default now(),
audience uuid[] null -- many to many table omitted for brevity
);
create table comments (
id serial primary key,
post_id int not null references posts(id) on delete cascade,
user_id uuid not null references auth.users(id),
body text not null,
comment_date date not null default now()
);
create policy "Creator can see their own posts"
on posts
for select
using (
auth.uid() = posts.creator_id
);
create policy "Logged in users can see the posts if they belong to the post 'audience'."
on posts
for select
using (
auth.uid() = any (posts.audience)
);
create policy "Users can see all comments for posts they have access to."
on comments
for select
using (
exists (
select 1 from posts
where posts.id = comments.post_id
)
);

Tips#

Disable realtime for private tables#

Our realtime server doesn't provide per-user security. Until we build a more robust auth system for WebSockets, you can disable realtime functionality for any private tables. To do this, you can manage the underlying Postgres replication publication:

/**
* REALTIME SUBSCRIPTIONS
* Only allow realtime listening on public tables.
*/
begin;
-- remove the realtime publication
drop publication if exists supabase_realtime;
-- re-create the publication but don't enable it for any tables
create publication supabase_realtime;
commit;
-- add a table to the publication
alter publication supabase_realtime add table products;
-- add other tables to the publication
alter publication supabase_realtime add table posts;

We're in the process of building enhanced realtime security.

You don't have to use policies#

You can also put your authorization rules in your middleware, similar to how you would create security rules with any other backend <-> middleware <-> frontend architecture.

Policies are a tool. In the case of "serverless/Jamstack" setups, they are especially effective because you don't have to deploy any middleware at all.

However, if you want to use another authorization method for your applications, that's also fine. Supabase is "just Postgres", so if your application works with Postgres, then it also works with Supabase.

Tip: Make sure to enable RLS for all your tables, so that your tables are inaccessible. Then use the "Service" which we provide, which is designed to bypass RLS.

Never use a service key on the client#

Supabase provides special "Service" keys, which can be used to bypass all RLS. These should never be used in the browser or exposed to customers, but they are useful for administrative tasks.