Allow declaring controller callbacks for certain routes

This makes it more convenient to execute callbacks only for certain
routes, by allowing usage of `:only` and `:except` keyword arguments.

This should play nicely with the recent instrumentation change, as the
user will see route names in the logs.

README.md

@@ -253,7 +253,7 @@ end
 ```
 ```rb
 class RodauthController < ApplicationController
-  before_action :set_locale # executes before Rodauth endpoints
+  before_action :verify_captcha, only: :login, if: -> { request.post? } # executes before Rodauth endpoints
   rescue_from("MyApp::SomeError") { |exception| ... } # rescues around Rodauth endpoints
 end
 ```

lib/rodauth/rails/feature/callbacks.rb

@@ -7,6 +7,8 @@ module Callbacks
         private
 
         def _around_rodauth
+          rails_controller_instance.instance_variable_set(:@_action_name, current_route.to_s)
+
           rails_controller_around { super }
         end
 

test/integration/callbacks_test.rb

@@ -5,18 +5,26 @@ class CallbacksTest < IntegrationTest
     visit "/login"
 
     assert_match "login-form", page.html
-    assert_equal 200,          page.status_code
-    assert_equal "true",       page.response_headers["X-Before-Action"]
-    assert_equal "true",       page.response_headers["X-After-Action"]
-    assert_equal "true",       page.response_headers["X-Before-Around-Action"]
-    assert_equal "true",       page.response_headers["X-After-Around-Action"]
+    assert_equal 200, page.status_code
+    assert_equal "true", page.response_headers["X-Before-Action"]
+    assert_equal "true", page.response_headers["X-After-Action"]
+    assert_equal "true", page.response_headers["X-Before-Around-Action"]
+    assert_equal "true", page.response_headers["X-After-Around-Action"]
+  end
+
+  test "runs callbacks for specific actions" do
+    visit "/create-account"
+    assert_equal "true", page.response_headers["X-Before-Specific-Action"]
+
+    visit "/login"
+    assert_nil page.response_headers["X-Before-Specific-Action"]
   end
 
   test "handles rendering in callback chain" do
     visit "/login?early_return=true&fail=true"
 
     assert_equal "early return", page.html
-    assert_equal 201,            page.status_code
-    assert_equal "true",         page.response_headers["X-Before-Action"]
+    assert_equal 201, page.status_code
+    assert_equal "true", page.response_headers["X-Before-Action"]
   end
 end

test/rails_app/app/controllers/rodauth_controller.rb

@@ -2,6 +2,7 @@ class RodauthController < ApplicationController
   before_action :before_route
   after_action :after_route
   around_action :around_route
+  before_action :before_specific_route, only: [:create_account]
 
   rescue_from NotImplementedError do
     render plain: "rescued response", status: 500
@@ -27,6 +28,10 @@ def around_route
     response.headers["X-After-Around-Action"] = "true"
   end
 
+  def before_specific_route
+    response.header["X-Before-Specific-Action"] = "true"
+  end
+
   def some_method
     "controller method"
   end