What is a presigned URL?
In short
- A presigned URL is a temporary, cryptographically signed link that grants access to one file in cloud storage for a limited time.
- It lets a private bucket serve a file without being made public.
- Modern hosts use it to share files securely without exposing the rest of their storage.
A presigned URL is a link that carries its own permission. Cloud storage like Cloudflare R2 or Amazon S3 keeps files in private buckets that nobody can open by default. To let someone reach one file, the system generates a URL signed with a secret key and stamped with an expiry time. Whoever holds that URL can fetch that single file until it expires, and nothing else. Access stays narrow and temporary, and the bucket never becomes public.
This is the plumbing behind secure sharing. A file you put online as a PDF sits in private storage, and access goes out through signed URLs instead of an open bucket. The signature means nobody can forge the link, and the expiry means a leaked link stops working after a while. Large platforms use the same mechanism to serve private uploads.
You never see any of this. You get a clean, friendly link, and the signing and expiry happen underneath. The idea connects to expiry dates on a share link, where you decide how long access lasts. Every plan works this way, from the free one to NudgeHost's paid plans, so the bucket behind your files stays private whatever you pay.
Related terms
Frequently asked questions
Is the share link I get a presigned URL?
Your friendly nudgehost.com link sits in front of the storage. Access to the underlying file goes through signed, expiring URLs, so the storage stays private.
Why not just make the storage public?
A public bucket exposes everything in it. Signed URLs grant access to one file at a time for a limited window, which is far safer.
Does the signature stop someone guessing my link?
The cryptographic signature cannot be forged, so nobody can fabricate a working URL. Combined with expiry, that keeps access tightly scoped.
Put it into practice.
Drop a file and get a shareable link in seconds. Free, no card needed.