Cannot get AWS API Gateway to override response codes - FitBit endpoint verification - amazon-web-services

Question

I am integrating FitBit with my company's platform and we are switching over from syncing with our own server to sending the data to an AWS Kinesis stream. This requires us to also set up an AWS API Gateway with a POST method to write the data to the stream. I've also set up a GET method on the same resource for the verification process.
Here's the problem I'm facing:
Once I have the API Endpoint properly set up, FitBit provides a verification code and requires a verification process in which it sends a GET request to the endpoint with a ?verify={correctVerificaitonCode} query param and wants a 204 response, and one with a ?verify={incorrectVericationCode} param and wants a 404 response. This would obviously be easy for me to accomplish in our Rails backend, where I'm in control of the code, but on AWS it's a tangled mess with little control.
I have read endless documentation on AWS about Mapping Templates and Integration Response, but no matter what I do, I cannot get the API to respond with anything other than a 200 (when the request is clean and has any ?verify param) or 500 (when I purposefully make a bad request). There is no straightforward answer in the AWS docs about this.
This is the closest I have come to a setup that the docs promise should work, yet it does not:
Using the Integration Response HTTP Status Regex
And with this mapping template
I'm two days in on this and frustrated to my wits' end. Help!

Answer 1

Just in case anyone find this thread in the future and is struggling with the same issue - here is how you verify a FitBit Developer API app with an Amazon Kinesis stream being fed by an AWS API Gateway:
First, set up the POST method of your API - there are AWS guides to this. Select AWS service as the integration type and kinesis as the service, then set up a mapping template for 'application/json' to look like this:
#set($event = $input.body)
#set($data = '{"action":' + $event +', "authorization": "' + $input.params('Authorization') + '", "stage":"' + $context.stage + '"}')
#set($body = $util.base64Encode($data))
{
"Data": "$body",
"PartitionKey": "shard-1",
"StreamName": "gm-fitbit"
}
Once you've done that, create a GET method on the same resource. Set MOCK as the integration type and create the endpoint. Now click on the GET method and visit Method Request. Expand URL Query String Parameters and add verify as a query param. Now, go back to the method and visit Integration Response.
Under the already existing 200 response method, expand it and add an HTTP status regex of 2\d{2} and passthrough handling.
Expand Mapping Templates, and for 'application/json' create this mapping template:
{
#if( $input.params('verify') == "theVerificationCodeProvidedToYouByFitbit" )
#set($context.responseOverride.status = 204)
#else
#set($context.responseOverride.status = 404)
#end
}
That's it! Deploy the API again, head back to Fitbit, and click verify!
There. Now there is officially a guide online to integrating Fitbit with an AWS Kinesis stream, the one I wish I had when struggling with this for 3 days.
Cheers!