Add ssh banner to ssh-auth-methods

nselib/libssh2-utility.lua

@@ -147,6 +147,23 @@ function SSHConnection:list (username)
   return false
 end
 
+---
+-- Attempt to retrieve the server's pre-auth banner
+--
+-- Need to attempt auth first (for instance by calling list)
+--
+-- @return The server's banner or nil on failure.
+function SSHConnection:banner ()
+  if not self.session then
+    return nil
+  end
+  local status, banner = pcall(libssh2.userauth_banner, self.session)
+  if status then
+    return banner
+  end
+  return nil
+end
+
 ---
 -- Attempts to read public key file
 --