docs: def authenticate_through_netrc(path=None):
      """
      Return the tuple user / password given a path for the .netrc file.
  
      Raises CredentialsError if no valid netrc file is found.
      """
      errors = []
      netrc_machine = 'coursera-dl'
      paths = [path] if path else get_config_paths("netrc")
      for path in paths:
          try:
              logging.debug('Trying netrc file %s', path)
              auths = netrc.netrc(path).authenticators(netrc_machine)
          except (IOError, netrc.NetrcParseError) as e:
              errors.append(e)
          else:
              if auths is None:
                  errors.append('Didn\'t find any credentials for ' +
                                netrc_machine)
              else:
                  return auths[0], auths[2]
  
      error_messages = '\n'.join(str(e) for e in errors)
      raise CredentialsError(
          'Did not find valid netrc file:\n' + error_messages +
          '\nPlease run this command: chmod og-rw ~/.netrc')