handler.py

import os
import json
import boto3
import hmac
import hashlib
import datetime
from urllib import parse
import logging
logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
TOKYO = 'ap-northeast-1'
# Get credentials
secret_name = os.environ['SLACK_API_SIGNING_SECRET']
secretsmanager = boto3.client('secretsmanager', region_name=TOKYO)
resp = secretsmanager.get_secret_value(SecretId=secret_name)
secret = json.loads(resp['SecretString'])


def verify(headers, body):
    try:
        signature = headers["X-Slack-Signature"]
        request_ts = int(headers["X-Slack-Request-Timestamp"])
        now_ts = int(datetime.datetime.now().timestamp())
        message = "v0:{}:{}".format(headers["X-Slack-Request-Timestamp"], body)
        expected = "v0={}".format(hmac.new(
                        bytes(secret['key'], 'UTF-8'),
                        bytes(message, 'UTF-8'),
                        hashlib.sha256).hexdigest())
    except Exception:
        return False
    else:
        if (abs(request_ts - now_ts) > (60 * 5)
                or not hmac.compare_digest(expected, signature)):
            return False
        return True


def request(event, context):
    if verify(event['headers'], event['body']):
        text = parse.parse_qs(event['body'])['text'][0]
        payload = {
            "text": 'Hello' + text,
        }
        response = {
            "statusCode": 200,
            "body": json.dumps(payload)
        }
        return response
    else:
        logger.info("Error: verify request")
        return {"statusCode": 400}