Using JClouds, up to version 1.6.x it was possible to access to the native EC2 provider API by using the following idiom:
AWSEC2Client ec2Client = AWSEC2Client.class.cast(context.getProviderSpecificContext().getApi());
Actually, I copied from the documentation page: http://jclouds.apache.org/guides/aws/
It turns out that in the latest release this method has been removed. Is there an alternative method/way to access to the provider specific features (security groups, key-pairs, etc)?