Returns the x509 public cert of the SP.
        :returns: SP public cert
        :rtype: string or None

def get_sp_cert(self):
        """
        Returns the x509 public cert of the SP.
        :returns: SP public cert
        :rtype: string or None
        """
        cert = self.__sp.get('x509cert')
        cert_file_name = self.__paths['cert'] + 'sp.crt'

        if not cert and exists(cert_file_name):
            with open(cert_file_name) as f:
                cert = f.read()

        return cert or None