Need to define apiKeySource for ApiGateway with custom authorizer

Hi,

I would like to be able to provide the ability to have my customer authorizer be the source of the api key, as per the aws docs

https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-lambda-authorizer-output.html
https://docs.aws.amazon.com/apigateway/api-reference/resource/rest-api/#apiKeySource

Event though there is no reference to this setting in the serverless docs, I have tried setting the value in the global provider settings

provider:
    apiGateway:
        apiKeySource: AUTHORIZER

However the cloud formation template does not produce any result with this, which was kind of expected.

"ApiGatewayRestApi": {
    "Type": "AWS::ApiGateway::RestApi",
    "Properties": {
        "Name": "test-api-gateway-dev",
        "EndpointConfiguration": {
            "Types": [
                "REGIONAL"
            ]
        }
    }
}

This should be technically possible, I am wondering if there is any support for this? or if serverless enforces the use of the HEADER value which then requires the key to be provided int the x-api-key header.