AppSync (CF): Does DbClusterIdentifier expect an ARN or a name?

Hi,

I have a question about the DbClusterIdentifier field for AppSync RelationalDatabase RdsHttpEndpointConfig (https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-appsync-datasource-relationaldatabaseconfig-rdshttpendpointconfig.html)

Doc states: "The database cluster identifier of the rdshttpendpoint."
But it seems not to be working, and instead, it should be the cluster's ARN.
See this issue: https://github.com/sid88in/serverless-appsync-plugin/issues/232

Is the doc wrong?

Bonus question:
How to get a Cluster's ARN from CF? According to the doc: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-rds-dbcluster.html
Neither Ref, nor Fn::GetAtt expose it.

Thank you