R + httr and EC2 api authentication issues

I would like to use the R package httr to access the EC2 services via their API. But I am a little bit unsure how to get started as it does not fall into the usual authentication format of "Oauth2.0" in which you have the usual: key, secret, token and signature system. I think EC2 uses the "signature version 2" method, but I am unclear as to how that works. to acces