drakkan/sftpgo ? reverse-engineered prompt

I need a flexible file transfer server. It should let users upload and download files using various methods like SFTP, FTP/S, and even a simple web browser interface for people who aren't technical.

The key feature is that I want to connect it to different storage backends. For example, when a user uploads a file via SFTP, I want the file to be saved directly to my S3 bucket, Google Cloud Storage, or an Azure Blob container, not the server's local disk.

Please also build a web-based admin panel for it. I'll need this to manage everything – creating user accounts, setting their permissions (like which folders they can access), and connecting to my different cloud storage providers. It should be a complete solution for bridging old-school file transfer protocols with modern cloud storage.