Using GraphQL client to access AWS AppSync protected by IAM security

This doesn't really live here but wanted to log something for anyone that comes looking for a solution to using this client with AWS AppSync. Feel free to close this.

I have a [gist available](https://gist.github.com/NeilBostrom/cab8b9275e39bb90ecf8e06ab980664b) that shows using the built-in [AWS4Signer](https://github.com/aws/aws-sdk-net/blob/master/sdk/src/Core/Amazon.Runtime/Internal/Auth/AWS4Signer.cs) to access an AppSync GraphQL endpoint protected by [AWS_IAM authorization](https://docs.aws.amazon.com/appsync/latest/devguide/security.html).