Pre-signed URLs are used to provide short-term access to a private object in your S3 bucket. They work by appending an AWS Access Key, expiration time, and Sigv4 signature as query parameters to the S3 object. There are two common use cases when you may want to use them: Simple, occasional sharing of private files.

What is the main advantage to a pre-signed URL?

A presigned URL gives you access to the object identified in the URL, provided that the creator of the presigned URL has permissions to access that object.

How secure are pre-signed URLs?

Presigned URLs do not provide authentication

In other words, presigned URLs only provide authorization to access a specific object in a bucket (and eventually impose some restrictions to that access) but the authentication is implicitly connected to the IAM role that generates the presigned link.