ioutil is deprecated in Go 1.16 and SFTPGo is an application, not
a library, we have no reason to keep compatibility with old Go
versions.
Go 1.16 fix some cifs related issues too.
HTTP clients are used for executing hooks such as the ones used for custom
actions, external authentication and pre-login user modifications.
This allows, for example, to use self-signed certificate without defeating the
purpose of using TLS
