Behaviour describing the API for public key handling of an SSH server. By implementing
    the callbacks defined in this behavior, the public key handling of an SSH server can
    be customized. By default the SSH application implements this behavior
    with help of the standard OpenSSH files,
    see the 
Type definitions that are used more than once in this module,
    or abstractions to indicate the intended use of the data
    type, or both. For more details on public key data types,
    refer to Section 2 Public Key Records in the
    
Fetches the private key of the host.
Checks if the user key is authorized.