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.
Always enable Row Level Security on tables, views, and functions in the public schema to protect your data.
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:
- Go to the Authentication > Policies page in the Dashboard.
- 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.
Any table without RLS enabled in the public schema will be accessible to the public, using the anon role. Always make sure that RLS is enabled or that you've got other security measures in place to avoid unauthorized access to your project's data!
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
publicschema.
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:
_10create function public.check_request()_10 returns void_10 language plpgsql_10 security definer_10 as $$_10begin_10 -- your logic here_10end;_10$$;
And register it to run on every Data API request using:
_10alter role authenticator_10 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:
_10notify 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:
_10raise sqlstate 'PGRST' using_10 message = json_build_object(_10 'code', '123',_10 'message', 'Payment Required',_10 'details', 'Quota exceeded',_10 'hint', 'Upgrade your plan')::text,_10 detail = json_build_object(_10 'status', 402,_10 'headers', json_build_object(_10 'X-Powered-By', 'Nerd Rage'))::text;
When raised within the public.check_request function, the resulting HTTP response will look like:
_10HTTP/1.1 402 Payment Required_10Content-Type: application/json; charset=utf-8_10X-Powered-By: Nerd Rage_10_10{_10 "message": "Payment Required",_10 "details": "Quota exceeded",_10 "hint": "Upgrade your plan",_10 "code": "123"_10}
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:
_10-- To get all the headers sent in the request_10SELECT current_setting('request.headers', true)::json;_10_10-- To get a single header, you can use JSON arrow operators_10SELECT current_setting('request.headers', true)::json->>'user-agent';_10_10-- Access Cookies_10SELECT current_setting('request.cookies', true)::json;
current_setting() | Example | Description |
|---|---|---|
request.method | GET, HEAD, POST, PUT, PATCH, DELETE | Request's method |
request.path | table | Table's path |
request.path | view | View's path |
request.path | rpc/function | Functions'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:
_10SELECT split_part(_10 current_setting('request.headers', true)::json->>'x-forwarded-for',_10 ',', 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_limitstable 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:
_10create table private.rate_limits (_10 ip inet,_10 request_at timestamp_10);_10_10-- add an index so that lookups are fast_10create 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:
_35create function public.check_request()_35 returns void_35 language plpgsql_35 security definer_35 as $$_35declare_35 req_method text := current_setting('request.method', true);_35 req_ip inet := split_part(_35 current_setting('request.headers', true)::json->>'x-forwarded-for',_35 ',', 1)::inet;_35 count_in_five_mins integer;_35begin_35 if req_method = 'GET' or req_method = 'HEAD' or req_method is null then_35 -- rate limiting can't be done on GET and HEAD requests_35 return;_35 end if;_35_35 select_35 count(*) into count_in_five_mins_35 from private.rate_limits_35 where_35 ip = req_ip and request_at between now() - interval '5 minutes' and now();_35_35 if count_in_five_mins > 100 then_35 raise sqlstate 'PGRST' using_35 message = json_build_object(_35 'message', 'Rate limit exceeded, try again after a while')::text,_35 detail = json_build_object(_35 'status', 420,_35 'status_text', 'Enhance Your Calm')::text;_35 end if;_35_35 insert into private.rate_limits (ip, request_at) values (req_ip, now());_35end;_35 $$;
Finally, configure the public.check_request() function to run on every Data API request:
_10alter role authenticator_10 set pgrst.db_pre_request = 'public.check_request';_10_10notify pgrst, 'reload config';
To clear old entries in the private.rate_limits table, set up a pg_cron job to clean them up.