RAG with Permissions
Fine-grain access control with Retrieval Augmented Generation.
Since pgvector is built on top of Postgres, you can implement fine-grain access control on your vector database using Row Level Security (RLS). This means you can restrict which documents are returned during a vector similarity search to users that have access to them. Supabase also supports Foreign Data Wrappers (FDW) which means you can use an external database or data source to determine these permissions if your user data doesn't exist in Supabase.
Use this guide to learn how to restrict access to documents when performing retrieval augmented generation (RAG).
Example
In a typical RAG setup, your documents are chunked into small subsections and similarity is performed over those sections:
_16-- Track documents/pages/files/etc_16create table documents (_16 id bigint primary key generated always as identity,_16 name text not null,_16 owner_id uuid not null references auth.users (id) default auth.uid(),_16 created_at timestamp with time zone not null default now()_16);_16_16-- Store the content and embedding vector for each section in the document_16-- with a reference to original document (one-to-many)_16create table document_sections (_16 id bigint primary key generated always as identity,_16 document_id bigint not null references documents (id),_16 content text not null,_16 embedding vector (384)_16);
Notice how we record the owner_id on each document. Let's create an RLS policy that restricts access to document_sections based on whether or not they own the linked document:
_12-- enable row level security_12alter table document_sections enable row level security;_12_12-- setup RLS for select operations_12create policy "Users can query their own document sections"_12on document_sections for select to authenticated using (_12 document_id in (_12 select id_12 from documents_12 where (owner_id = (select auth.uid()))_12 )_12);
In this example, the current user is determined using the built-in auth.uid() function when the query is executed through your project's auto-generated REST API. If you are connecting to your Supabase database through a direct Postgres connection, see Direct Postgres Connection below for directions on how to achieve the same access control.
Now every select query executed on document_sections will implicitly filter the returned sections based on whether or not the current user has access to them.
For example, executing:
_10select * from document_sections;
as an authenticated user will only return rows that they are the owner of (as determined by the linked document). More importantly, semantic search over these sections (or any additional filtering for that matter) will continue to respect these RLS policies:
_10-- Perform inner product similarity based on a match_threshold_10select *_10from document_sections_10where document_sections.embedding <#> embedding < -match_threshold_10order by document_sections.embedding <#> embedding;
The above example only configures select access to users. If you wanted, you could create more RLS policies for inserts, updates, and deletes in order to apply the same permission logic for those other operations. See Row Level Security for a more in-depth guide on RLS policies.
Alternative scenarios
Every app has its own unique requirements and may differ from the above example. Here are some alternative scenarios we often see and how they are implemented in Supabase.
Documents owned by multiple people
Instead of a one-to-many relationship between users and documents, you may require a many-to-many relationship so that multiple people can access the same document. Let's reimplement this using a join table:
_10create table document_owners (_10 id bigint primary key generated always as identity,_10 owner_id uuid not null references auth.users (id) default auth.uid(),_10 document_id bigint not null references documents (id)_10);
Then your RLS policy would change to:
_10create policy "Users can query their own document sections"_10on document_sections for select to authenticated using (_10 document_id in (_10 select document_id_10 from document_owners_10 where (owner_id = (select auth.uid()))_10 )_10);
Instead of directly querying the documents table, we query the join table.
User and document data live outside of Supabase
You may have an existing system that stores users, documents, and their permissions in a separate database. Let's explore the scenario where this data exists in another Postgres database. We'll use a foreign data wrapper (FDW) to connect to the external DB from within your Supabase DB:
RLS is latency-sensitive, so extra caution should be taken before implementing this method. Use the query plan analyzer to measure execution times for your queries to ensure they are within expected ranges. For enterprise applications, contact enterprise@supabase.io.
For data sources other than Postgres, see Foreign Data Wrappers for a list of external sources supported today. If your data lives in a source not provided in the list, please contact support and we'll be happy to discuss your use case.
Let's assume your external DB contains a users and documents table like this:
_12create table public.users (_12 id bigint primary key generated always as identity,_12 email text not null,_12 created_at timestamp with time zone not null default now()_12);_12_12create table public.documents (_12 id bigint primary key generated always as identity,_12 name text not null,_12 owner_id bigint not null references public.users (id),_12 created_at timestamp with time zone not null default now()_12);
In your Supabase DB, let's create foreign tables that link to the above tables:
_16create schema external;_16create extension postgres_fdw with schema extensions;_16_16-- Setup the foreign server_16create server foreign_server_16 foreign data wrapper postgres_fdw_16 options (host '<db-host>', port '<db-port>', dbname '<db-name>');_16_16-- Map local 'authenticated' role to external 'postgres' user_16create user mapping for authenticated_16 server foreign_server_16 options (user 'postgres', password '<user-password>');_16_16-- Import foreign 'users' and 'documents' tables into 'external' schema_16import foreign schema public limit to (users, documents)_16 from server foreign_server into external;
This example maps the authenticated role in Supabase to the postgres user in the external DB. In production, it's best to create a custom user on the external DB that has the minimum permissions necessary to access the information you need.
On the Supabase DB, we use the built-in authenticated role which is automatically used when end users make authenticated requests over your auto-generated REST API. If you plan to connect to your Supabase DB over a direct Postgres connection instead of the REST API, you can change this to any user you like. See Direct Postgres Connection for more info.
We'll store document_sections and their embeddings in Supabase so that we can perform similarity search over them via pgvector.
_10create table document_sections (_10 id bigint primary key generated always as identity,_10 document_id bigint not null,_10 content text not null,_10 embedding vector (384)_10);
We maintain a reference to the foreign document via document_id, but without a foreign key reference since foreign keys can only be added to local tables. Be sure to use the same ID data type that you use on your external documents table.
Since we're managing users and authentication outside of Supabase, we have two options:
- Make a direct Postgres connection to the Supabase DB and set the current user every request
- Issue a custom JWT from your system and use it to authenticate with the REST API
Direct Postgres connection
You can directly connect to your Supabase Postgres DB using the connection info on your project's database settings page. To use RLS with this method, we use a custom session variable that contains the current user's ID:
_12-- enable row level security_12alter table document_sections enable row level security;_12_12-- setup RLS for select operations_12create policy "Users can query their own document sections"_12on document_sections for select to authenticated using (_12 document_id in (_12 select id_12 from external.documents_12 where owner_id = current_setting('app.current_user_id')::bigint_12 )_12);
The session variable is accessed through the current_setting() function. We name the variable app.current_user_id here, but you can modify this to any name you like. We also cast it to a bigint since that was the data type of the user.id column. Change this to whatever data type you use for your ID.
Now for every request, we set the user's ID at the beginning of the session:
_10set app.current_user_id = '<current-user-id>';
Then all subsequent queries will inherit the permission of that user:
_10-- Only document sections owned by the user are returned_10select *_10from document_sections_10where document_sections.embedding <#> embedding < -match_threshold_10order by document_sections.embedding <#> embedding;
You might be tempted to discard RLS completely and simply filter by user within the where clause. Though this will work, we recommend RLS as a general best practice since RLS is always applied even as new queries and application logic is introduced in the future.
Custom JWT with REST API
If you would like to use the auto-generated REST API to query your Supabase database using JWTs from an external auth provider, you can get your auth provider to issue a custom JWT for Supabase.
See the Clerk Supabase docs for an example of how this can be done. Modify the instructions to work with your own auth provider as needed.
Now we can simply use the same RLS policy from our first example:
_12-- enable row level security_12alter table document_sections enable row level security;_12_12-- setup RLS for select operations_12create policy "Users can query their own document sections"_12on document_sections for select to authenticated using (_12 document_id in (_12 select id_12 from documents_12 where (owner_id = (select auth.uid()))_12 )_12);
Under the hood, auth.uid() references current_setting('request.jwt.claim.sub') which corresponds to the JWT's sub (subject) claim. This setting is automatically set at the beginning of each request to the REST API.
All subsequent queries will inherit the permission of that user:
_10-- Only document sections owned by the user are returned_10select *_10from document_sections_10where document_sections.embedding <#> embedding < -match_threshold_10order by document_sections.embedding <#> embedding;
Other scenarios
There are endless approaches to this problem based on the complexities of each system. Luckily Postgres comes with all the primitives needed to provide access control in the way that works best for your project.
If the examples above didn't fit your use case or you need to adjust them slightly to better fit your existing system, feel free to reach out to support and we'll be happy to assist you.