Rather than having to configure credentials explicitly, I'd like to use the IAM user execution role permissions.
http://docs.aws.amazon.com/lambda/latest/dg/intro-permission-model.html
I've simulated that this works fine. However, dynasty needs explicit credentials, and using process.env credentials doesn't work in Lambda, see this thread:
https://gist.github.com/cmawhorter/3cf67164414c4a97fcd8