In your UI let the user choose the item to download (for example a document entry). Each item should be referenced by the stored path or ID recorded in the item’s metadata.

From the client, invoke your backend’s download action for that file. The backend should verify the requesting user’s authorization and any business rules (ownership, expiration, role checks).

If authorized, your server either (A) streams the file from storage and returns it directly to the client, or (B) returns a short, internal path that the client can call to start the proxied download.

• Streaming keeps control entirely on the server.
• Return appropriate headers (Content-Type, Content-Length if known) and Content-Disposition for filename and inline/attachment behavior.

For web:

• Use a normal link or programmatically create a hidden link and set the href to the server download action (open in new tab or set the download attribute). For mobile or single-page apps:
• Use a fetch-like request to stream and save to local storage or present a progress UI.

Show retry UI, handle slow connections, and differentiate authorization failures vs network errors. Keep logs on the server for failed attempts if you need auditing.

Record successful downloads if required for compliance. If files are temporary, consider a short server cache or immediate eviction after delivery.

When the user clicks download, the client asks your backend for a presigned URL for that file. The backend must check user permissions first.

The server generates a presigned GET link with:

• A short expiration time (TTL).
• Response headers (Content-Disposition, Content-Type) encoded so the storage returns the right filename and behavior.
• Optional constraints (single-use, limited IPs if supported by your storage provider). Return that URL to the client.

The client uses the presigned URL directly in the browser or app. Options:

• Open in a new tab or anchor link (recommended for browser downloads).
• Use a native download manager or fetch for progress/resume if building custom UI.

Presigned URLs expire. If a client’s URL expires, have the client request a fresh one. Handle 403/404 responses as “not authorized” or “link expired”.

Because download bytes bypass your server, make sure you log when you issue presigned URLs and use access logs on storage to monitor actual downloads if needed.

Set short TTLs for sensitive files, and prefer single-use generation patterns (generate on-demand, do not reuse long-lived presigned links).

When a file is uploaded, capture its size so you can make decisions later (proxy vs presign).

For very large files, prefer presigned URLs and client-side range requests or a download manager that supports resuming, since this avoids moving the entire payload through your server.

Ensure the storage supports byte-range GETs and that the client can request partial ranges. If your UX must support pause/resume, use range headers and store progress client-side.

If uploads are part of the flow, avoid single-shot huge uploads. Chunked uploads reduce the chance that a single failure forces a full retry and make the file available progressively.

If you need server-side authorization but want direct transfer, consider issuing a short-lived presigned URL and returning a redirect to the client so the download starts immediately without the server streaming bytes.

Detect common failure modes (network drop, partial content responses) and show the user resume/retry options. Provide guidance such as “try a wired connection” for very large downloads on mobile.

Show a clear download button with file name, size, and type. If the file may be large, note expected download time.

Before fetching bytes, call your backend to validate access and to obtain either the proxied path or the presigned URL.

For browser downloads, setting an anchor href to the returned URL and using the download attribute (when supported) is the simplest way to ensure the correct filename.

If you use a programmatic fetch to stream data, show a progress indicator and allow cancel/resume for large transfers.

If a presigned URL fails (expired or blocked), present a friendly error and a button to retry obtaining a new link.

Mobile apps should leverage native download managers or built-in viewers. Opening large downloads in the background and notifying the user when complete prevents blocking the app UI.