There is no native support for SFTP and Apple isn't really putting much effort in that area (the CFFTP API was deprecated with iOS 9).
As you are new to Objective-C and Swift, your best bet is to find a third-party SFTP library that doesn't rely on CFFTPStream. Creating a SFTP client is not a project for beginners.
There is no native support for SFTP …
If you have the choice, use SFTP. FTPS fixes the security problems with FTP, but doesn’t fix all of its other deficiencies.
Or, better yet, use HTTPS, which has lots of other benefits, not least of which is standard support in the OS.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"