Fix webfinger returning wrong status code on malformed or missing param (#13759)

Fixes #13757

app/controllers/well_known/webfinger_controller.rb

@@ -8,7 +8,8 @@ module WellKnown
     before_action :set_account
     before_action :check_account_suspension
 
-    rescue_from ActiveRecord::RecordNotFound, ActionController::ParameterMissing, with: :not_found
+    rescue_from ActiveRecord::RecordNotFound, with: :not_found
+    rescue_from ActionController::ParameterMissing, WebfingerResource::InvalidRequest, with: :bad_request
 
     def show
       expires_in 3.days, public: true
@@ -37,6 +38,10 @@ module WellKnown
       expires_in(3.minutes, public: true) && gone if @account.suspended?
     end
 
+    def bad_request
+      head 400
+    end
+
     def not_found
       head 404
     end

app/lib/webfinger_resource.rb

@@ -3,6 +3,8 @@
 class WebfingerResource
   attr_reader :resource
 
+  class InvalidRequest < StandardError; end
+
   def initialize(resource)
     @resource = resource
   end
@@ -14,7 +16,7 @@ class WebfingerResource
     when /\@/
       username_from_acct
     else
-      raise(ActiveRecord::RecordNotFound)
+      raise InvalidRequest
     end
   end