This is exactly what I've been working on with Filestash (https://github.com/mickael-kerjean/filestash). It lets you connect to any kind of storage protocol that possible exist from S3, SFTP, FTS, SMB, NFS, Sharepoint, .... and layers its own fine grained permission control / chroots that integrate through SSO / RBAC so you can enforce access rules around who can do what and where (MCP doc: https://www.filestash.app/docs/api/#mcp)