From https://once.com/writebook

app/models/qr_code_link.rb

@@ -0,0 +1,26 @@
+class QrCodeLink
+  attr_reader :url
+
+  def initialize(url)
+    @url = url
+  end
+
+  def signed
+    self.class.verifier.generate(@url, purpose: :qr_code)
+  end
+
+  def self.from_signed(signed)
+    new verifier.verify(signed, purpose: :qr_code)
+  end
+
+  private
+    class << self
+      def verifier
+        ActiveSupport::MessageVerifier.new(secret, url_safe: true)
+      end
+
+      def secret
+        Rails.application.key_generator.generate_key("qr_codes")
+      end
+    end
+end