This CloudFormation template creates an API Gateway that will pass all JSON data sent as a PUT request to Kinesis Firehose which in turn deposits the data into S3.
aws cloudformation describe-stacks --stack-name <STACK_NAME> --query Stacks[].Outputs[].[OutputKey,OutputValue]
curl -X PUT -H 'Content-Type: application/json' -d '{"event":"sent"}' https://xd8tc7fim2.execute-api.us-east-1.amazonaws.com/prod