Create a help desk application to generate an Amazon S3 presigned URL for each employee. Configure the presigned URLs to have short expirations. Instruct employees to contact the company help desk to receive a presigned URL to access the S3 bucket.

Create a group for Amazon S3 access in IAM Identity Center. Add the employees who require access to the S3 bucket to the group. Create an IAM policy to allow Amazon S3 access from the group. Instruct employees to use the AWS access portal to access the AWS Management Console and navigate to the S3 bucket.

Create an Amazon S3 File Gateway. Create one share for data uploads and a second share for data downloads. Set up an SFTP service on an Amazon EC2 instance. Mount the shares to the EC2 instance. Instruct employees to use the SFTP server.

Configure AWS Transfer Family SFTP endpoints. Select the custom identity provider option. Use AWS Secrets Manager to manage the user credentials. Instruct employees to use Transfer Family SFTP.