REST API

Securing your API


The data APIs are designed to work with Postgres Row Level Security (RLS). If you use Supabase Auth, you can restrict data based on the logged-in user.

To control access to your data, you can use Policies.

Enabling row level security

Any table you create in the public schema will be accessible via the Supabase Data API.

To restrict access, enable Row Level Security (RLS) on all tables, views, and functions in the public schema. You can then write RLS policies to grant users access to specific database rows or functions based on their authentication token.

Any table created through the Supabase Dashboard will have RLS enabled by default. If you created the tables via the SQL editor or via another way, enable RLS like so:

  1. Go to the Authentication > Policies page in the Dashboard.
  2. Select Enable RLS to enable Row Level Security.

With RLS enabled, you can create Policies that allow or disallow users to access and update data. We provide a detailed guide for creating Row Level Security Policies in our Authorization documentation.

Disable the API or restrict to custom schema

If you don't use the Data API, or if you don't want to expose the public schema, you can either disable it entirely or change the automatically exposed schema to one of your choice. See Hardening the Data API for instructions.

Enforce additional rules on each request

Using Row Level Security policies may not always be adequate or sufficient to protect APIs.

Here are some common situations where additional protections are necessary:

  • Enforcing per-IP or per-user rate limits.
  • Checking custom or additional API keys before allowing further access.
  • Rejecting requests after exceeding a quota or requiring payment.
  • Disallowing direct access to certain tables, views or functions in the public schema.

You can build these cases in your application by creating a Postgres function that will read information from the request and perform additional checks, such as counting the number of requests received or checking that an API key is already registered in your database before serving the response.

Define a function like so:

create function public.check_request()
returns void
language plpgsql
security definer
as $$
begin
-- your logic here
end;
$$;

And register it to run on every Data API request using:

alter role authenticator
set pgrst.db_pre_request = 'public.check_request';

This configures the public.check_request function to run on every Data API request. To have the changes take effect, you should run:

notify pgrst, 'reload config';

Inside the function you can perform any additional checks on the request headers or JWT and raise an exception to prevent the request from completing. For example, this exception raises a HTTP 402 Payment Required response with a hint and additional X-Powered-By header:

raise sqlstate 'PGRST' using
message = json_build_object(
'code', '123',
'message', 'Payment Required',
'details', 'Quota exceeded',
'hint', 'Upgrade your plan')::text,
detail = json_build_object(
'status', 402,
'headers', json_build_object(
'X-Powered-By', 'Nerd Rage'))::text;

When raised within the public.check_request function, the resulting HTTP response will look like:

HTTP/1.1 402 Payment Required
Content-Type: application/json; charset=utf-8
X-Powered-By: Nerd Rage

{
"message": "Payment Required",
"details": "Quota exceeded",
"hint": "Upgrade your plan",
"code": "123"
}

Use the JSON operator functions to build rich and dynamic responses from exceptions.

If you use a custom HTTP status code like 419, you can supply the status_text key in the detail clause of the exception to describe the HTTP status.

If you're using PostgREST version 11 or lower (find out your PostgREST version) a different and less powerful syntax needs to be used.

Accessing request information

Like with RLS policies, you can access information about the request by using the current_setting() Postgres function. Here are some examples on how this works:

-- To get all the headers sent in the request
SELECT current_setting('request.headers', true)::json;

-- To get a single header, you can use JSON arrow operators
SELECT current_setting('request.headers', true)::json->>'user-agent';

-- Access Cookies
SELECT current_setting('request.cookies', true)::json;
current_setting()ExampleDescription
request.methodGET, HEAD, POST, PUT, PATCH, DELETERequest's method
request.pathtableTable's path
request.pathviewView's path
request.pathrpc/functionFunctions's path
request.headers{ "User-Agent": "...", ... }JSON object of the request's headers
request.cookies{ "cookieA": "...", "cookieB": "..." }JSON object of the request's cookies
request.jwt{ "sub": "a7194ea3-...", ... }JSON object of the JWT payload

To access the IP address of the client look up the X-Forwarded-For header in the request.headers setting. For example:

SELECT split_part(
current_setting('request.headers', true)::json->>'x-forwarded-for',
',', 1); -- takes the client IP before the first comma (,)

Read more about PostgREST's pre-request function.

Examples

You can only rate-limit POST, PUT, PATCH and DELETE requests. This is because GET and HEAD requests run in read-only mode, and will be served by Read Replicas which do not support writing to the database.

Outline:

  • A new row is added to a private.rate_limits table each time a modifying action is done to the database containing the IP address and the timestamp of the action.
  • If there are over 100 requests from the same IP address in the last 5 minutes, the request is rejected with a HTTP 420 code.

Create the table:

create table private.rate_limits (
ip inet,
request_at timestamp
);

-- add an index so that lookups are fast
create index rate_limits_ip_request_at_idx on private.rate_limits (ip, request_at desc);

The private schema is used as it cannot be accessed over the API!

Create the public.check_request function:

create function public.check_request()
returns void
language plpgsql
security definer
as $$
declare
req_method text := current_setting('request.method', true);
req_ip inet := split_part(
current_setting('request.headers', true)::json->>'x-forwarded-for',
',', 1)::inet;
count_in_five_mins integer;
begin
if req_method = 'GET' or req_method = 'HEAD' or req_method is null then
-- rate limiting can't be done on GET and HEAD requests
return;
end if;

select
count(*) into count_in_five_mins
from private.rate_limits
where
ip = req_ip and request_at between now() - interval '5 minutes' and now();

if count_in_five_mins > 100 then
raise sqlstate 'PGRST' using
message = json_build_object(
'message', 'Rate limit exceeded, try again after a while')::text,
detail = json_build_object(
'status', 420,
'status_text', 'Enhance Your Calm')::text;
end if;

insert into private.rate_limits (ip, request_at) values (req_ip, now());
end;
$$;

Finally, configure the public.check_request() function to run on every Data API request:

alter role authenticator
set pgrst.db_pre_request = 'public.check_request';

notify pgrst, 'reload config';

To clear old entries in the private.rate_limits table, set up a pg_cron job to clean them up.