What's the best place for storing reserved usernames in CodeIgniter?

I'm developing a website and want to implement a feature that prevents users from creating accounts with certain reserved usernames like "account," "index," "profile," and others. I have already compiled a list of these reserved usernames, but I'm unsure about the best place to store this data/array within CodeIgniter.
As someone who is familiar with CodeIgniter, I prefer to adhere to its recommended structure and organization. However, I'm uncertain whether storing an array of reserved usernames in helpers, libraries, or configs is the appropriate approach. I don't want to deviate from best practices.
I would greatly appreciate any suggestions on where to store this array within the CodeIgniter framework. Thank you in advance for your assistance!