A company receives data transfers from a small number of external clients that use SFTP software on an Amazon EC2 instance. The clients use an SFTP client to upload data. The clients use SSH keys for authentication. Every hour, an automated script transfers new uploads to an Amazon S3 bucket for processing. The company wants to move the transfer process to an AWS managed service and to reduce the time required to start data processing. The company wants to retain the existing user management and SSH key generation process. The solution must not require clients to make significant changes to their existing processes. Which solution will meet these requirements?