Use Twilio API with lambda function over AWS API Gateway.

twilio_lambda_function.py

import base64
import json
import os
import urllib
from urllib import request, parse


TWILIO_SMS_URL = "https://api.twilio.com/2010-04-01/Accounts/{}/Messages.json"
TWILIO_CALL_URL = "https://api.twilio.com/2010-04-01/Accounts/{}/Calls.json"
TWILIO_ACCOUNT_SID = os.environ.get("TWILIO_ACCOUNT_SID")
TWILIO_AUTH_TOKEN = os.environ.get("TWILIO_AUTH_TOKEN")


def lambda_handler(event, context):
    # json body
    to_number = event['To']
    from_number = event['From']
    body = event['Body']
    action = event['Action']

    if not TWILIO_ACCOUNT_SID:
        return "Unable to access Twilio Account SID."
    elif not TWILIO_AUTH_TOKEN:
        return "Unable to access Twilio Auth Token."
    elif not to_number:
        return "The function needs a 'To' number in the format +12023351493"
    elif not from_number:
        return "The function needs a 'From' number in the format +19732644156"
    elif not body:
        return "The function needs a 'Body' message to send."
    elif not action:
        return "The function needs a 'Action' SMS/WhatsApp/Call."

    if action == "WHATSAPP":
        from_number = "whatsapp:" + from_number
        to_number   = "whatsapp:" + to_number

    # insert Twilio Account SID into the REST API URL
    if action == "CALL":
        populated_url = TWILIO_CALL_URL.format(TWILIO_ACCOUNT_SID)
        post_params = {"To": to_number, "From": from_number, "Url": body}
    else:
        populated_url = TWILIO_SMS_URL.format(TWILIO_ACCOUNT_SID)
        post_params = {"To": to_number, "From": from_number, "Body": body}
    

    

    # encode the parameters for Python's urllib
    data = parse.urlencode(post_params).encode()
    req = request.Request(populated_url)

    # add authentication header to request based on Account SID + Auth Token
    authentication = "{}:{}".format(TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN)
    base64string = base64.b64encode(authentication.encode('utf-8'))
    req.add_header("Authorization", "Basic %s" % base64string.decode('ascii'))

    try:
        # perform HTTP POST request
        with request.urlopen(req, data) as f:
            print("Twilio returned {}".format(str(f.read().decode('utf-8'))))
    except Exception as e:
        # something went wrong!
        return e

    return action + " successfully!"