Switch to a single message verifier

No need for this proliferation

app/models/active_storage/variation.rb

@@ -2,17 +2,15 @@
 
 # A set of transformations that can be applied to a blob to create a variant.
 class ActiveStorage::Variation
-  class_attribute :verifier
-
   attr_reader :transformations
 
   class << self
     def decode(key)
-      new verifier.verify(key)
+      new ActiveStorage.verifier.verify(key)
     end
 
     def encode(transformations)
-      verifier.generate(transformations)
+      ActiveStorage.verifier.generate(transformations)
     end
   end
 

app/models/active_storage/verified_key_with_expiration.rb

 class ActiveStorage::VerifiedKeyWithExpiration
-  class_attribute :verifier
-
   class << self
     def encode(key, expires_in: nil)
-      verifier.generate([ key, expires_at(expires_in) ])
+      ActiveStorage.verifier.generate([ key, expires_at(expires_in) ])
     end
 
     def decode(encoded_key)
-      key, expires_at = verifier.verified(encoded_key)
+      key, expires_at = ActiveStorage.verifier.verified(encoded_key)
 
       key if key && fresh?(expires_at)
     end

lib/active_storage.rb

@@ -6,4 +6,6 @@ module ActiveStorage
 
   autoload :Blob
   autoload :Service
+
+  mattr_accessor :verifier
 end

lib/active_storage/engine.rb

@@ -22,14 +22,9 @@ class Engine < Rails::Engine # :nodoc:
       end
     end
 
-    initializer "active_storage.verifiers" do
-      require "active_storage/verified_key_with_expiration"
-      require "active_storage/variation"
-
+    initializer "active_storage.verifier" do
       config.after_initialize do |app|
-        ActiveStorage::VerifiedKeyWithExpiration.verifier = \
-        ActiveStorage::Variation.verifier = \
-          Rails.application.message_verifier("ActiveStorage")
+        ActiveStorage.verifier = Rails.application.message_verifier("ActiveStorage")
       end
     end
 

test/test_helper.rb

@@ -33,6 +33,7 @@
 
 require "active_storage/variation"
 ActiveStorage::Variation.verifier = ActiveSupport::MessageVerifier.new("Testing")
+ActiveStorage.verifier = ActiveSupport::MessageVerifier.new("Testing")
 
 class ActiveSupport::TestCase
   private