It is possible to pass a string containing JSON instead of a hash. It makes possible to use Jedlik with builders such as Jbuilder or json_builder.
Time.now was called multiple times, resulting in a possibility that the value would be different for the signature generation and the timestamp request (memorization prevented this to happen, but caused other problems)
The POST request was not encoding parameters correctly.
signing requests requires access_key_id and secret_access_key