Alexa Smart Home Skill Adapter for Home Assistant

cloudformation-template.yaml

# To use this template, see the example CLI command below or use the AWS CloudFormation console at https://console.aws.amazon.com/cloudformation/home.
# aws cloudformation create-stack --stack-name homeassistant-skill --template-body file://lambda.yaml 
# --parameters ParameterKey=BaseUrl,ParameterValue=[XXX] ParameterKey=SkillId,ParameterValue=[XXX] --capabilities CAPABILITY_IAM
AWSTemplateFormatVersion: '2010-09-09'
Metadata: 
  Copyright: Justin McCormick <me@justinmccormick.com>
  License: Apache-2.0
Description: |
  This template creates a Lambda function that acts as a proxy between Alexa and Home Assistant.
  The Lambda was sourced from https://gist.github.com/matt2005/744b5ef548cc13d88d0569eea65f5e5b.
Parameters:
  BaseUrl:
    Type: String
    Description: Base URL of your Home Assistant instance, for example, https://your-home-assistant-instance.example.com
  SkillId:
    Type: String
    Description: Skill ID of your Alexa skill
  LongLivedAccessToken:
    Type: String
    Description: Long-lived access token of your Home Assistant instance
    Default: ''
  NotVerifySsl:
    Type: String
    Description: Whether to verify SSL certificate of your Home Assistant instance
    Default: 'false'
  Debug:
    Type: String
    Description: Whether to enable debug mode
    Default: 'false'
Resources:
  LambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Handler: index.lambda_handler
      Role: !GetAtt LambdaRole.Arn
      Runtime: python3.8
      Environment:
        Variables:
          BASE_URL: !Ref BaseUrl
          LONG_LIVED_ACCESS_TOKEN: !Ref LongLivedAccessToken
          NOT_VERIFY_SSL: !Ref NotVerifySsl
          DEBUG: !Ref Debug
      Code:
        ZipFile: |
          """
          Copyright 2019 Jason Hu <awaregit at gmail.com>

          Licensed under the Apache License, Version 2.0 (the "License");
          you may not use this file except in compliance with the License.
          You may obtain a copy of the License at

              http://www.apache.org/licenses/LICENSE-2.0

          Unless required by applicable law or agreed to in writing, software
          distributed under the License is distributed on an "AS IS" BASIS,
          WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
          See the License for the specific language governing permissions and
          limitations under the License.
          """
          import os
          import json
          import logging
          import urllib3

          _debug = bool(os.environ.get('DEBUG'))

          _logger = logging.getLogger('HomeAssistant-SmartHome')
          _logger.setLevel(logging.DEBUG if _debug else logging.INFO)


          def lambda_handler(event, context):
              """Handle incoming Alexa directive."""
              
              _logger.debug('Event: %s', event)

              base_url = os.environ.get('BASE_URL')
              assert base_url is not None, 'Please set BASE_URL environment variable'
              base_url = base_url.strip("/")

              directive = event.get('directive')
              assert directive is not None, 'Malformatted request - missing directive'
              assert directive.get('header', {}).get('payloadVersion') == '3', \
                  'Only support payloadVersion == 3'
              
              scope = directive.get('endpoint', {}).get('scope')
              if scope is None:
                  # token is in grantee for Linking directive 
                  scope = directive.get('payload', {}).get('grantee')
              if scope is None:
                  # token is in payload for Discovery directive 
                  scope = directive.get('payload', {}).get('scope')
              assert scope is not None, 'Malformatted request - missing endpoint.scope'
              assert scope.get('type') == 'BearerToken', 'Only support BearerToken'

              token = scope.get('token')
              if token is None and _debug:
                  token = os.environ.get('LONG_LIVED_ACCESS_TOKEN')  # only for debug purpose
              
              verify_ssl = not bool(os.environ.get('NOT_VERIFY_SSL'))
              
              http = urllib3.PoolManager(
                  cert_reqs='CERT_REQUIRED' if verify_ssl else 'CERT_NONE',
                  timeout=urllib3.Timeout(connect=2.0, read=10.0)
              )
              
              response = http.request(
                  'POST', 
                  '{}/api/alexa/smart_home'.format(base_url),
                  headers={
                      'Authorization': 'Bearer {}'.format(token),
                      'Content-Type': 'application/json',
                  },
                  body=json.dumps(event).encode('utf-8'),
              )
              if response.status >= 400:
                  return {
                      'event': {
                          'payload': {
                              'type': 'INVALID_AUTHORIZATION_CREDENTIAL' 
                                      if response.status in (401, 403) else 'INTERNAL_ERROR',
                              'message': response.data.decode("utf-8"),
                          }
                      }
                  }
              _logger.debug('Response: %s', response.data.decode("utf-8"))
              return json.loads(response.data.decode('utf-8'))
  LambdaRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Version: '2012-10-17'
        Statement:
          - Effect: Allow
            Principal:
              Service: lambda.amazonaws.com
            Action: sts:AssumeRole
      Path: /
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole

  AlexaSkillNameEventPermission:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:invokeFunction
      FunctionName: !GetAtt LambdaFunction.Arn
      Principal: alexa-appkit.amazon.com
      EventSourceToken: !Ref SkillId