We are trying to deploy a SAM app to respond to Slack slash-commands. When you deploy a AWS::Serverless::Function with an Api event source, you get an API Gateway with a proxy lambda — so HTTP POST requests are relayed verbatim to the Lambda under apiGatewayRequestBody. Slack posts parameters as application/x-www-form-urlencoded, but ApiGatewayRequest's FromJSON instance requires the body to be JSON-formatted.

This all means that there is no (simple) way to use aws-lambda-haskell-runtime with AWS SAM to receive the Slack payload. I've forked this repository to add the functionality I need, but I am not convinced my solution will work for everyone so I'm not willing to submit a PR yet.