code: def _negotiate_value(response):
      
      if hasattr(_negotiate_value, 'regex'):
          regex = _negotiate_value.regex
      else:
          # There's no need to re-compile this EVERY time it is called. Compile
          # it once and you won't have the performance hit of the compilation.
          regex = re.compile('(?:.*,)*\s*Negotiate\s*([^,]*),?', re.I)
          _negotiate_value.regex = regex
  
      authreq = response.headers.get('www-authenticate', None)
  
      if authreq:
          match_obj = regex.search(authreq)
          if match_obj:
              return match_obj.group(1)
  
      return None
docs: Extracts the gssapi authentication token from the appropriate header