Feature Request: Custom API KEY

In the Api Gateway service, you can easily create custom Api keys with a specific value (See [AWS::ApiGateway::ApiKey](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-apigateway-apikey.html))

That is something that is currently missing in Appsync (See [AWS::AppSync::ApiKey](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-appsync-apikey.html))

It would be useful to be able to set API keys with custom values, to ensure that re-creation of the service will not break any client using those keys.

This is slightly related to https://github.com/aws/aws-appsync-community/issues/5
In general, AppSync is currently a quite dangerous service to use if for any reason the API needs to be re-created.

EDIT:
In addition to this, I would like to add that we need true unauthenticated access with AppSync.
The only only reason we use API_KEY is because we need anonymous access to the api.
I know using API key is the "recommended"way of handling unauthenticated access, but this sounds more like a workaround to me. Api key, by definition, **IS** authentication.
This has already been discussed many times. The api key solution comes with several issues. One of them is what I just described in this post.

Start with the AWS::AppSync::ApiKey documentation linked in the issue and compare it with AWS::ApiGateway::ApiKey. Review the related issue #5 and the existing discussion to clarify whether the request covers stable custom key values, true unauthenticated access, or both; done requires an agreed scope and documented AppSync support.

Written by the indexing model from the issue text.