Behaviour describing the API for an SSH server's public key handling. By implementing the callbacks defined
    in this behavior it is possible to customize the SSH server's public key
    handling. By default the SSH application implements this behavior
    with help of the standard openssh files, see 
Type definitions that are used more than once in this module
    and/or abstractions to indicate the intended use of the data
    type. For more details on public key data types 
    see the 
boolean() = true | false
string() = [byte()]
public_key() = #'RSAPublicKey'{} | {integer(), #'Dss-Parms'{}} | term()
private_key() = #'RSAPrivateKey'{} | #'DSAPrivateKey'{} | term()
public_key_algorithm() = 'ssh-rsa' | 'ssh-dss' | atom()
Fetches the hosts private key
Checks if the user key is authorized