class Aws::Signers::V4

def signature(request, datetime, body_digest)
  k_secret = @credentials.secret_access_key
  k_date = hmac("AWS4" + k_secret, datetime[0,8])
  k_region = hmac(k_date, @region)
  k_service = hmac(k_region, @service_name)
  k_credentials = hmac(k_service, 'aws4_request')
  hexhmac(k_credentials, string_to_sign(request, datetime, body_digest))
end