Supabase storage permissions: test private file access

Direct answer

For supabase storage row level security, use a reproducible fixture, explicit expected outcomes and evidence of the final business state. A hidden download link is not an access policy; test the file request and write path with separate identities.

This is a scoped method for a founder or agency reviewing an existing app or integration. It defines test expectations; it does not describe an audit performed on a client system.

Define the fixture and policy

Place private files under tenant-owned paths in a synthetic storage bucket.

Use an authorized test environment and synthetic records. Record the release, identities, initial state and dependency conditions. Replace the example policy with your approved product policy before running the checks. If the required outcome is undecided, resolve that decision before classifying the implementation as defective.

Worked example and acceptance matrix

All rows begin NOT RUN. The expectations belong to this example, not every product or provider. Preserve fail and blocked results rather than counting an unavailable dependency as a pass.

Run the conditions independently

1. Owner read

Set up this condition deliberately rather than waiting for it to occur during an ordinary click-through. For this fixture, the acceptance condition is approved file is returned. Capture authenticated download and compare it with the agreed initial state. A different result needs a reproduction record; missing access to that evidence makes the case blocked. Keep the condition separate from the other rows so one successful case cannot conceal a failure here.

2. Other tenant read

Set up this condition deliberately rather than waiting for it to occur during an ordinary click-through. For this fixture, the acceptance condition is private file is denied. Capture response and object identity and compare it with the agreed initial state. A different result needs a reproduction record; missing access to that evidence makes the case blocked. Keep the condition separate from the other rows so one successful case cannot conceal a failure here.

3. Forged upload path

Set up this condition deliberately rather than waiting for it to occur during an ordinary click-through. For this fixture, the acceptance condition is cross-tenant write is rejected. Capture storage object inventory and compare it with the agreed initial state. A different result needs a reproduction record; missing access to that evidence makes the case blocked. Keep the condition separate from the other rows so one successful case cannot conceal a failure here.

Save a reproducible test record

The following original fixture can be copied into a test plan. Its identifiers are synthetic. It contains no production credentials and does not make network requests.

{
  "example": "synthetic; not executed",
  "scope": "Place private files under tenant-owned paths in a synthetic storage bucket.",
  "cases": [
    {
      "id": "day-38-case-1",
      "condition": "Owner read",
      "expected": "Approved file is returned",
      "evidence": "Authenticated download",
      "status": "NOT RUN"
    },
    {
      "id": "day-38-case-2",
      "condition": "Other tenant read",
      "expected": "Private file is denied",
      "evidence": "Response and object identity",
      "status": "NOT RUN"
    },
    {
      "id": "day-38-case-3",
      "condition": "Forged upload path",
      "expected": "Cross-tenant write is rejected",
      "evidence": "Storage object inventory",
      "status": "NOT RUN"
    }
  ]
}

Add the actual result, a redacted evidence reference and the environment after execution. Reset state between cases that mutate records. When a response is uncertain, inspect the business receipt or persisted state before repeating the action.

Interpret the result and choose the next step

A hidden download link is not an access policy; test the file request and write path with separate identities.

A failure report should name the affected condition, the observed difference and its business impact. A blocked result should name the missing dependency and its owner. After a repair, rerun the original failure and a relevant ordinary path against the new release. Keep untested conditions visible. This matrix does not establish exhaustive security, compliance, performance or integration coverage.

Use the paired tool

Supabase RLS Checklist Builder provides a practical companion. Its dated enhancement is storage read and write cases. The planning worksheet creates named cases and exports your recorded outcomes; it does not automatically exercise your app. Use the tool's existing calculation or validation separately where relevant.

Implementation reference

Consult Supabase storage access control for the underlying platform or method. The source is an implementation reference; the fixture and product expectations above are original illustrative conditions, not quoted provider guarantees. Confirm the documentation for your deployed version before implementation.

Frequently asked questions

What demonstrates owner read?

For this fixture, approved file is returned. Inspect authenticated download; a success message alone may not establish the approved outcome.

What if other tenant read cannot be reproduced?

Record it as blocked with the missing setup or dependency. Do not replace the missing evidence with the image or a generated expectation. The diagram is instructional, and this article reports no executed result.

When is a scoped review useful?

Request one when a critical condition fails, ownership is unclear or the team cannot determine what committed. Bring the reproduction and agreed policy.

Recommended action

Start with the matrix for supabase storage row level security, then record evidence before accepting or repairing the result. Discuss a scoped AI app audit or book a discovery call. Share the stack and broken journey in the initial enquiry; arrange any required access separately.