Features such as SFTP on Shifter are made available through the WordPress Dashboard using Plugins such as File Manager.
File Manager, adds the ability to upload, download, zip, copy and paste all from the WordPress backend.
This is particularly helpful during Child Theme development, uploads files while testing, browsing wp-content and more.
While using the File Manager WordPress Plugin uploads and download are securely transferred over HTTPS.
It's important to note that using the File Manager plugin comes without warranty as it's an open source plugin freely available in the official WordPress Plugin directory.