code: def get_sp_key(self):
          
          key = self.__sp.get('privateKey')
          key_file_name = self.__paths['cert'] + 'sp.key'
  
          if not key and exists(key_file_name):
              with open(key_file_name) as f:
                  key = f.read()
  
          return key or None
docs: Returns the x509 private key of the SP.
          :returns: SP private key
          :rtype: string or None