code: def get_bewit(resource):
      
      if resource.method != 'GET':
          raise ValueError('bewits can only be generated for GET requests')
      if resource.nonce != '':
          raise ValueError('bewits must use an empty nonce')
      mac = calculate_mac(
          'bewit',
          resource,
          None,
      )
  
      if isinstance(mac, six.binary_type):
          mac = mac.decode('ascii')
  
      if resource.ext is None:
          ext = ''
      else:
          validate_header_attr(resource.ext, name='ext')
          ext = resource.ext
  
      # b64encode works only with bytes in python3, but all of our parameters are
      # in unicode, so we need to encode them. The cleanest way to do this that
      # works in both python 2 and 3 is to use string formatting to get a
      # unicode string, and then explicitly encode it to bytes.
      inner_bewit = u"{id}\\{exp}\\{mac}\\{ext}".format(
          id=resource.credentials['id'],
          exp=resource.timestamp,
          mac=mac,
          ext=ext,
      )
      inner_bewit_bytes = inner_bewit.encode('ascii')
      bewit_bytes = urlsafe_b64encode(inner_bewit_bytes)
      # Now decode the resulting bytes back to a unicode string
      return bewit_bytes.decode('ascii')
docs: Returns a bewit identifier for the resource as a string.
  
      :param resource:
          Resource to generate a bewit for
      :type resource: `mohawk.base.Resource`