Redmine

I'am using a gem ntlm-sso. I want to use it in Redmine. As it is written in the instructions, I added new file in config/initializers/ntlm-sso.rb and adding the line config.middleware.use "NTLMAuthentication" to config/application.rb. It works, but I want to use it as a plugin, without changing the core code. How can I override application.rb and add new initializer as Redmine plugin?