When we try to connect to our Cerberus SFTP server with WinSCP and choose SCP as the File protocol we are getting Authentication failed.
SCP is a protocol built on the Secure Shell (SSH) infrastructure. It allows its users to transfer/copy files from a system to a remote location securely. SCP is primarily used within command-line interfaces.
WinSCP won't work as an SCP client because it isn't issuing pure SCP commands. It's trying to mix together a bunch of SSH capabilities. We generally recommend testing with command-line SCP clients simply because they tend to be limited to issuing just SCP commands.
SCP is an extremely simple protocol. It allows uploading a single file, downloading a single file, recursively downloading a folder, or recursively uploading a folder. That's it. There's no facility or commands built into the protocol for getting directory listings, or anything else that would allow a client to construct a file system interface for a user. It's meant for extremely simple use cases where you need to transfer one or more files or folders from point A to point B. If you want a user interface and the ability to browse a folder, you need to switch to SFTP.