Use CanCanCan for changeset comments

This introduces different deny_access handlers for web and api requests, since we want to avoid sending redirects as API responses. See #2064 for discussion.

app/controllers/application_controller.rb

@@ -477,7 +477,15 @@ class ApplicationController < ActionController::Base
     end
   end
 
-  def deny_access(_exception)
+  def deny_access(exception)
+    if @api_deny_access_handling
+      api_deny_access(exception)
+    else
+      web_deny_access(exception)
+    end
+  end
+
+  def web_deny_access(_exception)
     if current_token
       set_locale
       report_error t("oauth.permissions.missing"), :forbidden
@@ -497,6 +505,26 @@ class ApplicationController < ActionController::Base
     end
   end
 
+  def api_deny_access(_exception)
+    if current_token
+      set_locale
+      report_error t("oauth.permissions.missing"), :forbidden
+    elsif current_user
+      head :forbidden
+    else
+      realm = "Web Password"
+      errormessage = "Couldn't authenticate you"
+      response.headers["WWW-Authenticate"] = "Basic realm=\"#{realm}\""
+      render :plain => errormessage, :status => :unauthorized
+    end
+  end
+
+  attr_accessor :api_access_handling
+
+  def api_deny_access_handler
+    @api_deny_access_handling = true
+  end
+
   private
 
   # extract authorisation credentials from headers, returns user = nil if none

app/controllers/changeset_comments_controller.rb

@@ -3,8 +3,10 @@ class ChangesetCommentsController < ApplicationController
   before_action :authorize_web, :only => [:index]
   before_action :set_locale, :only => [:index]
   before_action :authorize, :only => [:create, :destroy, :restore]
-  before_action :require_moderator, :only => [:destroy, :restore]
-  before_action :require_allow_write_api, :only => [:create, :destroy, :restore]
+  before_action :api_deny_access_handler, :only => [:create, :destroy, :restore]
+
+  authorize_resource
+
   before_action :require_public_data, :only => [:create]
   before_action :check_api_writable, :only => [:create, :destroy, :restore]
   before_action :check_api_readable, :except => [:create, :index]