aws signature generator creates headers for the REST API for AWS-IOT shadows
aws-sign.c can run in an embedded environment (like ESP or Photon) so that REST can be used to get and update AWS-IOT shadows. This an alternative to using MQTT + TLS or a webhook. It does require secure storage of the AWS secret key.
It uses this sha2 code: https://github.com/mikejsavage/hmac. The sha256.c/h files are not included in this repository and have to be retrieved seperately.
shell-aws4-test.c provides a command line interface for aws-signing functions. The output is a valid curl command so it can be piped into a shell: shell-aws4-test [arguments] | bash
shell-aws4-test.c provides a -h option that describes the command line arguments.
The code has been tested on Mac OS X. The next step is to test with Photon and then maybe nodeMCU as a C library.