Example SAM template for API Gateway with Lambda proxy integration

example-apgiw-lambda-proxy.sam.yaml

AWSTemplateFormatVersion: '2010-09-09'
Transform: 'AWS::Serverless-2016-10-31'

Globals:
  Api:
    EndpointConfiguration: REGIONAL
    # Your CORS hosts need to be in this format - note the two layers of quotes.
    Cors: "'*'"

# Our Python callback
Resources:
  YourFunction:
    Type: AWS::Serverless::Function
    Properties:
      Handler: callbackcode.handler
      Runtime: python3.7
      CodeUri: ./yourfunction/
      Events:
        Callback:
          Type: Api
          Properties:
            Path: /yourcallback
            Method: get
            RestApiId:
              Ref: YourAPIGateway

  # Our callback API
  YourAPIGateway:
    Type: AWS::Serverless::Api
    DependsOn: YourFunction
    Properties:
      StageName: prod
      DefinitionBody:
        swagger: 2.0
        info:
          version: "1.0"
          title: "A nice title"
        basePath: /prod
        schemes:
        - "https"
        paths:
          /callback:
            get:
              responses: {}
              x-amazon-apigateway-integration:
                uri:
                  # You need to build up the ARN with this pattern - you can't just use a !Ref or !GetAtt AFAIK.
                  Fn::Sub: arn:${AWS::Partition}:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${YourFunction.Arn}/invocations
                passthroughBehavior: "when_no_match"
                httpMethod: "POST"
                type: "aws_proxy"

yourfunction.py

import json
import os

def handler(event, context):
     body = 'foo'

    # Now, send a 200 and include our event details.
    response = {
        'statusCode': 200,
        'body': body
    }


    # Ensure that this function can be called from wherever you want to (CORS headers).
    response["headers"] = {
        'Content-Type': 'application/json',
        'Access-Control-Allow-Origin': '*'
    }

    # Return our response object.
    return response

I got caught up on the CORS definition for quite a while. My deploys were failing and I was getting an inscrutable (to me) message:

Errors found during import: Unable to put integration response on 'OPTIONS' for resource at path '/callback': Invalid mapping expression specified: Validation Result: warnings : [], errors : [Invalid mapping expression specified: *]

I found on another gist someone mentioned debugging with sam local start-api --debug, which helped a lot! So, try that if your template fails, it may help track it down.

@cam8001
Remember 2 quotes

Cors: "'*'"

I have a question, how to set a response in 'responses' key?

paths:
/callback:
get:
responses: {#here}
x-amazon-apigateway-integration:
uri:

I only write the code? example: responses:{200}