Add application config for URL-safe Base64 CSRF tokens

This allows applications to safely upgrade to Rails 6.1 without
breaking tokens while the deploy is still being rolled out.

actionpack/CHANGELOG.md

@@ -83,7 +83,7 @@
     out of the box: the value has to be url-encoded and decoded to survive transport.
 
     Now, we generate Base64 urlsafe-encoded CSRF tokens, which are inherently safe
-    to transport.  Validation accepts both urlsafe tokens, and strict-encoded tokens
+    to transport. Validation accepts both urlsafe tokens, and strict-encoded tokens
     for backwards compatibility.
 
     *Scott Blum*

actionpack/lib/action_controller/metal/request_forgery_protection.rb

@@ -90,6 +90,10 @@ module RequestForgeryProtection
       config_accessor :default_protect_from_forgery
       self.default_protect_from_forgery = false
 
+      # Controls whether URL-safe CSRF tokens are generated.
+      config_accessor :urlsafe_csrf_tokens, instance_writer: false
+      self.urlsafe_csrf_tokens = false
+
       helper_method :form_authenticity_token
       helper_method :protect_against_forgery?
     end
@@ -329,7 +333,7 @@ def valid_authenticity_token?(session, encoded_masked_token) # :doc:
         end
 
         begin
-          masked_token = Base64.urlsafe_decode64(encoded_masked_token)
+          masked_token = decode_csrf_token(encoded_masked_token)
         rescue ArgumentError # encoded_masked_token is invalid Base64
           return false
         end
@@ -367,7 +371,7 @@ def mask_token(raw_token) # :doc:
         one_time_pad = SecureRandom.random_bytes(AUTHENTICITY_TOKEN_LENGTH)
         encrypted_csrf_token = xor_byte_strings(one_time_pad, raw_token)
         masked_token = one_time_pad + encrypted_csrf_token
-        Base64.urlsafe_encode64(masked_token, padding: false)
+        encode_csrf_token(masked_token)
       end
 
       def compare_with_real_token(token, session) # :doc:
@@ -393,8 +397,8 @@ def valid_per_form_csrf_token?(token, session) # :doc:
       end
 
       def real_csrf_token(session) # :doc:
-        session[:_csrf_token] ||= SecureRandom.urlsafe_base64(AUTHENTICITY_TOKEN_LENGTH, padding: false)
-        Base64.urlsafe_decode64(session[:_csrf_token])
+        session[:_csrf_token] ||= generate_csrf_token
+        decode_csrf_token(session[:_csrf_token])
       end
 
       def per_form_csrf_token(session, action_path, method) # :doc:
@@ -462,5 +466,33 @@ def normalize_action_path(action_path) # :doc:
         uri = URI.parse(action_path)
         uri.path.chomp("/")
       end
+
+      def generate_csrf_token # :nodoc:
+        if urlsafe_csrf_tokens
+          SecureRandom.urlsafe_base64(AUTHENTICITY_TOKEN_LENGTH, padding: false)
+        else
+          SecureRandom.base64(AUTHENTICITY_TOKEN_LENGTH)
+        end
+      end
+
+      def encode_csrf_token(csrf_token) # :nodoc:
+        if urlsafe_csrf_tokens
+          Base64.urlsafe_encode64(csrf_token, padding: false)
+        else
+          Base64.strict_encode64(csrf_token)
+        end
+      end
+
+      def decode_csrf_token(encoded_csrf_token) # :nodoc:
+        if urlsafe_csrf_tokens
+          Base64.urlsafe_decode64(encoded_csrf_token)
+        else
+          begin
+            Base64.strict_decode64(encoded_csrf_token)
+          rescue ArgumentError
+            Base64.urlsafe_decode64(encoded_csrf_token)
+          end
+        end
+      end
   end
 end

actionpack/test/controller/request_forgery_protection_test.rb

@@ -175,12 +175,15 @@ class SkipProtectionController < ActionController::Base
 # common test methods
 module RequestForgeryProtectionTests
   def setup
+    @old_urlsafe_csrf_tokens = ActionController::Base.urlsafe_csrf_tokens
+    ActionController::Base.urlsafe_csrf_tokens = true
     @token = Base64.urlsafe_encode64("railstestrailstestrailstestrails")
     @old_request_forgery_protection_token = ActionController::Base.request_forgery_protection_token
     ActionController::Base.request_forgery_protection_token = :custom_authenticity_token
   end
 
   def teardown
+    ActionController::Base.urlsafe_csrf_tokens = @old_urlsafe_csrf_tokens
     ActionController::Base.request_forgery_protection_token = @old_request_forgery_protection_token
   end
 
@@ -378,10 +381,25 @@ def test_should_allow_post_with_token
   end
 
   def test_should_allow_post_with_strict_encoded_token
-    session[:_csrf_token] = Base64.strict_encode64("railstestrailstestrailstestrails")
-    @controller.stub :form_authenticity_token, @token do
-      assert_not_blocked { post :index, params: { custom_authenticity_token: @token } }
+    token_length = (ActionController::RequestForgeryProtection::AUTHENTICITY_TOKEN_LENGTH * 4.0 / 3).ceil
+    token_including_url_unsafe_chars = "+/".ljust(token_length, "A")
+    session[:_csrf_token] = token_including_url_unsafe_chars
+    @controller.stub :form_authenticity_token, token_including_url_unsafe_chars do
+      assert_not_blocked { post :index, params: { custom_authenticity_token: token_including_url_unsafe_chars } }
+    end
+  end
+
+  def test_should_allow_post_with_urlsafe_token_when_migrating
+    config_before = ActionController::Base.urlsafe_csrf_tokens
+    ActionController::Base.urlsafe_csrf_tokens = false
+    token_length = (ActionController::RequestForgeryProtection::AUTHENTICITY_TOKEN_LENGTH * 4.0 / 3).ceil
+    token_including_url_safe_chars = "-_".ljust(token_length, "A")
+    session[:_csrf_token] = token_including_url_safe_chars
+    @controller.stub :form_authenticity_token, token_including_url_safe_chars do
+      assert_not_blocked { post :index, params: { custom_authenticity_token: token_including_url_safe_chars } }
     end
+  ensure
+    ActionController::Base.urlsafe_csrf_tokens = config_before
   end
 
   def test_should_allow_patch_with_token

guides/source/configuring.md

@@ -505,6 +505,8 @@ The schema dumper adds two additional configuration options:
 
 * `config.action_controller.default_protect_from_forgery` determines whether forgery protection is added on `ActionController::Base`. This is false by default.
 
+* `config.action_controller.urlsafe_csrf_tokens` configures whether generated CSRF tokens are URL-safe. Defaults to `false`.
+
 * `config.action_controller.relative_url_root` can be used to tell Rails that you are [deploying to a subdirectory](configuring.html#deploy-to-a-subdirectory-relative-url-root). The default is `ENV['RAILS_RELATIVE_URL_ROOT']`.
 
 * `config.action_controller.permit_all_parameters` sets all the parameters for mass assignment to be permitted by default. The default value is `false`.
@@ -994,6 +996,7 @@ text/javascript image/svg+xml application/postscript application/x-shockwave-fla
 - `config.active_job.skip_after_callbacks_if_terminated`: `true`
 - `config.action_dispatch.cookies_same_site_protection`: `:lax`
 - `ActiveSupport.utc_to_local_returns_utc_offset_times`: `true`
+- `config.action_controller.urlsafe_csrf_tokens`: `true`
 
 #### For '6.0', new defaults from previous versions below and:
 

railties/lib/rails/application/configuration.rb

@@ -177,6 +177,10 @@ def load_defaults(target_version)
             action_dispatch.cookies_same_site_protection = :lax
           end
 
+          if respond_to?(:action_controller)
+            action_controller.urlsafe_csrf_tokens = true
+          end
+
           ActiveSupport.utc_to_local_returns_utc_offset_times = true
         else
           raise "Unknown version #{target_version.to_s.inspect}"

railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_1.rb.tt

@@ -25,6 +25,12 @@
 # It's best enabled when your entire app is migrated and stable on 6.1.
 # Rails.application.config.action_dispatch.cookies_same_site_protection = :lax
 
+# Generate CSRF tokens that are encoded in URL-safe Base64.
+#
+# This change is not backwards compatible with earlier Rails versions.
+# It's best enabled when your entire app is migrated and stable on 6.1.
+# Rails.application.config.action_controller.urlsafe_csrf_tokens = true
+
 # Specify whether `ActiveSupport::TimeZone.utc_to_local` returns a time with an
 # UTC offset or a UTC time.
 # ActiveSupport.utc_to_local_returns_utc_offset_times = true