WebDAV is supported by Windows, MacOS and Linux. On all platforms you can mount it without admin/sudo (`net use` on Windows, `mount_webdav` on macOS and `gio mount` on Linux). Here is official Go package[1] using which you can implement your own WebDAV server (you only need to implement your FS interface).
[1] https://pkg.go.dev/golang.org/x/net/webdav