What is the MOST operationally efficient solution that will meet this requirement?
Attach an S3 bucket policy that only allows object downloads from the users’ IP addresses.
Create an IAM role that has access to the object. Instruct the users to assume the role.
Create an IAM user that has access to the object. Share the credentials with the users.
Generate a presigned URL for the object. Share the URL with the users.
Explanations:
Attaching a bucket policy that allows access based on IP addresses does not resolve the issue of users lacking AWS accounts. It also requires managing IP addresses and may not be feasible if users are in different locations.
Creating an IAM role and instructing users to assume it is not practical since the users do not have AWS accounts. IAM roles are designed for AWS users or services, and external users without AWS accounts cannot assume a role.
Creating an IAM user and sharing credentials is not secure or efficient, as it involves creating AWS accounts for each user and managing those credentials, which can lead to security risks and operational overhead.
Generating a presigned URL allows temporary access to a specific S3 object without needing an AWS account. This method is simple, secure, and operationally efficient, as the URL can be shared directly with users for a limited time.
I would say the answer is:
Generate a presigned URL for the object. Share the URL with the users.