code: def generate_secret_header(secret, body)
        sha = OpenSSL::HMAC.hexdigest(OpenSSL::Digest::Digest.new('sha1'), secret, body)
        # GitHub sends it as 'X-Hub-Signature', but Rack provides it as HTTP_X_HUB_SIGNATURE... :/
        {'HTTP_X_HUB_SIGNATURE' => "sha1=#{sha}"}
      end
docs: :nodoc: