Problems Reading Cookies

* Framework version: 1.3.2
* Implementations: Spark

## Scenario
Lambda is fronted by API Gateway which is in turn fronted by cloudfront which is the host of the public vanity URL.

Code is the lambda is looking for a cookie but cannot get get. I assume that this is because it's not getting x-forwarded data? In a similar situation with a ELB running Spring/tomcat we had a similar problem and needed to add the following properties to Spring:

server.tomcat.remote-ip-header=x-forwarded-for
server.tomcat.protocol-header=x-forwarded-proto

I assume there is something like this for Spark? I don't see anything in their documentation?

## Expected behavior
Can read cookies on the vanity domain

## Actual behavior
no cookies :(

## Steps to reproduce
Create the above scenario

Thank You!

まず、リクエストが API Gateway と CloudFront を通過する際に、Cookie が Java Spark 実装にどのように公開されるかを追跡します。報告された vanity-domain のシナリオを、既存の serverless-java-container のドキュメントおよびリクエスト処理の動作と比較します。そのデプロイパスで Cookie を読み取れるようになれば完了です。

索引モデルが issue の本文から書いたものです。