code: def build_body(self, template_file=INDEX):
          
  
          if self.params['error'] == 'access_denied':
              message = docs.OAUTH_ACCESS_DENIED
          elif self.params['error'] is not None:
              message = docs.OAUTH_ERROR.format(error=self.params['error'])
          elif self.params['state'] is None or self.params['code'] is None:
              message = docs.OAUTH_INVALID
          else:
              message = docs.OAUTH_SUCCESS
  
          with codecs.open(template_file, 'r', 'utf-8') as fp:
              index_text = fp.read()
  
          body = string.Template(index_text).substitute(message=message)
          body = codecs.encode(body, 'utf-8')
          return body
docs: Params:
              template_file (text): Path to an index.html template
  
          Returns:
              body (bytes): THe utf-8 encoded document body