Are there any options to inject an object into the context called clientContext? The native mobile SDKs pass this in, which has device information, etc, as well as the local AWS Cognito identifier. This is the sort of information that will become more and more common once mobile developers start calling into Lambdas natively.
http://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html#API_Invoke_RequestSyntax
http://docs.aws.amazon.com/mobileanalytics/latest/ug/PutEvents.html