How to Safely Share Files Using AWS S3 Pre-Signed URLs

Jay Tillu

·May 28, 2025·

4 min read

🔎 What is a Pre-Signed URL?
🛠️ How Can You Generate It?
📦 Real-World Use Cases Arjun Found
⚠️ Important Notes for SAA Exam & Real Life
✅ Arjun’s Takeaway

One fine morning, Arjun was sipping his coffee when his project manager messaged:

“Hey Arjun, a client needs to download a report stored in our private S3 bucket. Can you make it happen?”

Arjun thought, “Hmm… I can’t make the file public — that would be a security risk.”

That’s when he remembered something from his AWS studies:
🎯 S3 Pre-Signed URLs

🔎 What is a Pre-Signed URL?

A Pre-Signed URL is a special URL that temporarily grants access to a private object in your S3 bucket — either to download (GET) or upload (PUT) a file.

✅ It inherits the permissions of the IAM identity that generated the URL.
✅ It expires after a set time — so it’s secure and time-bound.
✅ It requires no credentials for the end user.

🛠️ How Can You Generate It?

Arjun learned that he could generate these URLs using:

Tool	Max Expiry Time
AWS Console	Up to 12 hours
AWS CLI / SDK	Up to 7 days (168 hours)

He fired up the CLI and ran:

aws s3 presign s3://secure-bucket/reports/monthly.pdf --expires-in 3600

✅ That gave him a URL that worked for 1 hour.

📦 Real-World Use Cases Arjun Found

Here are some of Arjun’s favorite use cases:

🔐 Give external users temporary access to download a private file
Send them a pre-signed URL valid for a few hours.
📤 Let someone upload a file securely to a specific S3 location
Pre-sign a PUT request and restrict it to a path.
🎥 Stream a premium video only for logged-in users
Dynamically generate a new URL after each login.
🛠️ CI/CD tools pushing build logs or test results
Use pre-signed PUT URLs without exposing IAM credentials.

⚠️ Important Notes for SAA Exam & Real Life

Before using them in production, Arjun made sure to remember:

Pre-signed URLs are only valid for a specific operation (GET, PUT, etc.)
They’re secure only if you protect the URL — don’t share it publicly
Permissions are based on the IAM user or role that signs the URL
Good practice: Set a short expiration to reduce risk

✅ Arjun’s Takeaway

“Pre-signed URLs are like giving someone a key to a single door that works for a few minutes — super convenient and still secure.”

He sent the URL to the client, who downloaded the report instantly. No IAM roles, no bucket policy changes — just a simple, temporary URL.

📌 SAA Exam Tip

Expect at least one question involving S3 access control and pre-signed URLs. Remember:

URL is temporary
URL inherits signer’s permissions
Use for GET or PUT
Can be generated using CLI, SDK, or Console