'This extension is used by the client to define what signature algorithms
are preferred, including both the hash algorithm and the public key
algorithm, with a level of detail down to even the public key algorithm
parameters, such as curve name.
:return:
None or a PreferredSignatureAlgorithms object'

@property
def preferred_signature_algorithms_value(self):

    if (self._processed_extensions is False):
        self._set_extensions()
    return self._preferred_signature_algorithms_value
