'Get xml representation of the object.
@return: The root node.
@rtype: L{Element}'

def xml(self):

    root = Element('UsernameToken', ns=wssens)
    u = Element('Username', ns=wssens)
    u.setText(self.username)
    root.append(u)
    p = Element('Password', ns=wssens)
    p.setText(self.password)
    root.append(p)
    if (self.nonce is not None):
        n = Element('Nonce', ns=wssens)
        n.setText(self.nonce)
        root.append(n)
    if (self.created is not None):
        n = Element('Created', ns=wsuns)
        n.setText(str(UTC(self.created)))
        root.append(n)
    return root
