Signed URL
A signed URL is a URL that encodes a short-lived authorisation — who can read the file, and for how long — in its query string. Private files in cloud storage are not publicly readable; the server generates a signed URL on demand when a specific viewer is allowed to see the file.
Syndik8 uses signed URLs for usage-log photos. When a viewer opens a booking and is entitled to see the photo, the app generates a URL that is valid for 15 minutes. After that window the URL stops working. The signed URL cannot usefully be shared — it expires too fast — which is the point.
If a viewer is not entitled to see the photo, no URL is generated at all.