Security · Guide
A document download link is part of your permission system
Treat uploads, previews, and downloads as one access lifecycle.
The file is not just another field
In an illustrative onboarding app, staff remove a contractor from a project but a previously issued document URL remains usable. The permission screen and storage behavior now disagree. Before adding AI document extraction, define who may upload, preview, download, and delete each attachment. The extraction worker should inherit a narrow job permission rather than unrestricted access to every customer bucket.
Issue access after checking the request
A proposed download flow rechecks membership and document ownership, then issues short-lived access for one object. S3 presigned URLs are a mechanism for temporary access, not a substitute for deciding who deserves it. Keep object keys unrelated to public filenames where practical, and avoid logging the full signed link. Explain the remaining validity window if access is withdrawn after a URL has already been issued.
Workflow at a glance
Separate quarantine from availability
Use an upload staging area with size and type constraints, safe filenames, and content checks appropriate to the use case. Only mark a file available after the agreed checks complete. Do not let model processing make an unreviewed upload publicly retrievable. A failed extraction should leave a clear operational state, not trigger repeated uploads by confused users. Link derived artifacts back to the original authorization context.
Test removal and expiry
Test a removed user, a deleted attachment, an expired URL, a guessed identifier, and a large malformed upload with synthetic data. Document which copies may remain in backups and how they age out. A short link lifetime improves some exposure windows but does not prevent an authorized recipient from saving a copy. Choose the lifecycle based on actual document sensitivity and workflow needs instead of a blanket claim of secure file sharing.
Show the permission story
Demonstrate upload, preview, download, removal, and expiry with a synthetic document. Ask the customer owner what a former member can still access. If their understanding differs from the implementation, fix the interface or policy. Discuss locally saved copies as a separate boundary.
Sources and further reading
- Download and upload objects with presigned URLsDownload and upload objects with presigned URLsAWS · Documentation ·
- File Upload Cheat SheetFile Upload Cheat SheetOWASP · Documentation ·
Editorial approach
AI-assisted original writing, checked against linked public sources. Practical recommendations and illustrative scenarios are editorial analysis, not reported client results. Source dates and product details may differ from this collection’s preparation date.