Add Application#message_verifier method to return a message verifier

guides/source/4_1_release_notes.md

@@ -124,6 +124,17 @@ See
 [active_record/enum.rb](https://github.com/rails/rails/blob/4-1-stable/activerecord/lib/active_record/enum.rb#L2-L42)
 for a detailed write up.
 
+### Application message verifier.
+
+Create a message verifier that can be used to generate and verify signed
+messages in the application.
+
+```ruby
+message = Rails.application.message_verifier('salt').generate('my sensible data')
+Rails.application.message_verifier('salt').verify(message)
+# => 'my sensible data'
+```
+
 Documentation
 -------------
 
@@ -164,6 +175,7 @@ for detailed changes.
 
 * Exposed `MiddlewareStack#unshift` to environment configuration. ([Pull Request](https://github.com/rails/rails/pull/12479))
 
+* Add `Application#message_verifier` method to return a message verifier. ([Pull Request](https://github.com/rails/rails/pull/12995))
 
 Action Mailer
 -------------

railties/CHANGELOG.md

@@ -1,3 +1,20 @@
+*   Add `Application#message_verifier` method to return a message verifier.
+
+    This verifier can be used to generate and verify signed messages in the application.
+
+        message = Rails.application.message_verifier('salt').generate('my sensible data')
+        Rails.application.message_verifier('salt').verify(message)
+        # => 'my sensible data'
+
+    It is recommended not to use the same verifier for different things, so you can get different
+    verifiers passing the name argument.
+
+        message = Rails.application.message_verifier('cookies').generate('my sensible cookie data')
+
+    See the `ActiveSupport::MessageVerifier` documentation for more information.
+
+    *Rafael Mendonça França*
+
 *   The [Spring application
     preloader](https://github.com/jonleighton/spring) is now installed
     by default for new applications. It uses the development group of

railties/lib/rails/application.rb

@@ -1,6 +1,7 @@
 require 'fileutils'
 require 'active_support/core_ext/object/blank'
 require 'active_support/key_generator'
+require 'active_support/message_verifier'
 require 'rails/engine'
 
 module Rails
@@ -107,12 +108,13 @@ def inherited(base)
 
     def initialize(initial_variable_values = {}, &block)
       super()
-      @initialized      = false
-      @reloaders        = []
-      @routes_reloader  = nil
-      @app_env_config   = nil
-      @ordered_railties = nil
-      @railties         = nil
+      @initialized       = false
+      @reloaders         = []
+      @routes_reloader   = nil
+      @app_env_config    = nil
+      @ordered_railties  = nil
+      @railties          = nil
+      @message_verifiers = {}
 
       add_lib_to_load_path!
       ActiveSupport.run_load_hooks(:before_configuration, self)
@@ -158,6 +160,31 @@ def key_generator
       end
     end
 
+    # Returns a message verifier object.
+    #
+    # This verifier can be used to generate and verify signed messages in the application.
+    #
+    # It is recommended not to use the same verifier for different things, so you can get different
+    # verifiers passing the +verifier_name+ argument.
+    #
+    # ==== Parameters
+    #
+    # * +salt+ - the salt that will be used to generate the secret key of the verifier.
+    #
+    # ==== Examples
+    #
+    #     message = Rails.application.message_verifier('salt').generate('my sensible data')
+    #     Rails.application.message_verifier('salt').verify(message)
+    #     # => 'my sensible data'
+    #
+    # See the +ActiveSupport::MessageVerifier+ documentation for more information.
+    def message_verifier(salt)
+      @message_verifiers[salt] ||= begin
+        secret = key_generator.generate_key(salt)
+        ActiveSupport::MessageVerifier.new(secret)
+      end
+    end
+
     # Stores some of the Rails initial environment parameters which
     # will be used by middlewares and engines to configure themselves.
     def env_config

railties/test/application/configuration_test.rb

@@ -268,6 +268,41 @@ def index
       assert_equal 'some_value', verifier.verify(last_response.body)
     end
 
+    test "application verifier can be used in the entire application" do
+      make_basic_app do |app|
+        app.config.secret_key_base = 'b3c631c314c0bbca50c1b2843150fe33'
+        app.config.session_store :disabled
+      end
+
+      message = app.message_verifier('salt').generate("some_value")
+
+      assert_equal 'some_value', Rails.application.message_verifier('salt').verify(message)
+
+      secret = app.key_generator.generate_key('salt')
+      verifier = ActiveSupport::MessageVerifier.new(secret)
+      assert_equal 'some_value', verifier.verify(message)
+    end
+
+    test "application verifier can build different verifiers" do
+      make_basic_app do |app|
+        app.config.secret_key_base = 'b3c631c314c0bbca50c1b2843150fe33'
+        app.config.session_store :disabled
+      end
+
+      default_verifier = app.message_verifier('salt')
+      text_verifier = app.message_verifier('text')
+
+      message = text_verifier.generate('some_value')
+
+      assert_equal 'some_value', text_verifier.verify(message)
+      assert_raises ActiveSupport::MessageVerifier::InvalidSignature do
+        default_verifier.verify(message)
+      end
+
+      assert_equal default_verifier.object_id, app.message_verifier('salt').object_id
+      assert_not_equal default_verifier.object_id, text_verifier.object_id
+    end
+
     test "protect from forgery is the default in a new app" do
       make_basic_app