code: def _prepare_authorizer_event(self, arn, lambda_event, lambda_context):
          # type: (str, EventType, LambdaContext) -> EventType
          
          authorizer_event = lambda_event.copy()
          authorizer_event['type'] = 'TOKEN'
          try:
              authorizer_event['authorizationToken'] = authorizer_event.get(
                  'headers', {})['authorization']
          except KeyError:
              raise NotAuthorizedError(
                  {'x-amzn-RequestId': lambda_context.aws_request_id,
                   'x-amzn-ErrorType': 'UnauthorizedException'},
                  b'{"message":"Unauthorized"}')
          authorizer_event['methodArn'] = arn
          return authorizer_event
docs: Translate event for an authorizer input.