def sign_params(params, key)
      msg = Utils.normalize_params(params)
      digest = OpenSSL::Digest.new('sha256')
      OpenSSL::HMAC.hexdigest(digest, key, msg)
    end
def sign_params(params, key)
      msg = Utils.normalize_params(params)
      digest = OpenSSL::Digest.new('sha256')
      OpenSSL::HMAC.hexdigest(digest, key, msg)
    end
Given a Hash of parameters, normalize them (flatten and convert to a
 string), then generate the HMAC-SHA-256 signature using the provided key.

 @param [Hash] params the parameters to sign
 @param [String] key the key to sign the params with
 @return [String] the resulting signature