DEV: Add SecureUploadEndpointHelpers for controllers (#25758)

This commit moves some code out of UploadController#show_secure
so it can be reused in other controllers if a secure upload
needs to have permission checks run.

lib/secure_upload_endpoint_helpers.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+module SecureUploadEndpointHelpers
+  include ActiveSupport::Concern
+
+  def upload_from_path_and_extension(path_with_ext)
+    sha1 = File.basename(path_with_ext, File.extname(path_with_ext))
+    # this takes care of optimized image requests
+    sha1 = sha1.partition("_").first if sha1.include?("_")
+    Upload.find_by(sha1: sha1)
+  end
+
+  def upload_from_full_url(url)
+    Upload.find_by(sha1: Upload.sha1_from_long_url(url))
+  end
+
+  def check_secure_upload_permission(upload)
+    if upload.access_control_post_id.present?
+      raise Discourse::InvalidAccess if current_user.nil? && SiteSetting.login_required
+      raise Discourse::InvalidAccess if !guardian.can_see?(upload.access_control_post)
+    else
+      raise Discourse::NotFound if current_user.nil?
+    end
+  end
+end