Managing File Permissions and Security

Supabase Storage offers robust control over who can access your files. This is crucial for protecting sensitive data and ensuring your application behaves as expected. We achieve this through Row Level Security (RLS), a powerful feature that allows you to define policies for accessing data based on user roles and attributes.

When you create a new bucket in Supabase Storage, it automatically has RLS enabled. This means you need to explicitly define policies that grant permissions for users to interact with the files within that bucket. By default, no one can access anything, which is a secure starting point.

Let's explore how to set up some common permission scenarios. The core idea is to write SQL policies that are evaluated by Supabase for every file operation (upload, download, delete, list).

Consider a scenario where you want authenticated users to be able to upload files to a bucket named 'user-uploads'. You'd need a policy that allows them to perform the 'INSERT' operation on files within this bucket.

This policy allows any user whose role is 'authenticated' to insert objects into the storage.objects table. The WITH CHECK clause ensures that the operation only proceeds if the condition is met.

Now, what about downloading files? You might want authenticated users to download files, but perhaps only their own files. This requires a bit more logic.

In this example, we assume that when a file is uploaded, you store the user_id of the uploader in a column named owner_id within your metadata (or in a separate table linked to the file). The USING clause here allows a SELECT operation (which corresponds to downloading or listing) only if the authenticated user's ID (auth.uid()) matches the owner_id of the file.