'Given a list of authentication policy URIs that a provider
supports, this method returns the subsequence of those types
that are preferred by the relying party.
@param supported_types: A sequence of authentication policy
type URIs that are supported by a provider
@returns: The sub-sequence of the supported types that are
preferred by the relying party. This list will be ordered
in the order that the types appear in the supported_types
sequence, and may be empty if the provider does not prefer
any of the supported authentication types.
@returntype: [str]'

def preferredTypes(self, supported_types):

    return filter(self.preferred_auth_policies.__contains__, supported_types)
