need WooCommerce hook to generate authentication code with sale-complete email

I write utility software in c++ and need to add a user authorization code to the email that’s sent to the customer when the purchase (through Stripe) is complete. My best guess is that WC_Email_Customer_Completed_Order is the place where I’d add my custom PHP function to update my order database, generate the code, and add it to the customer’s email.

I’m sure this is asked often, but apologize that I’ve been unable to find any relevant posts. I’m new to WordPress and PHP, and any guidance or a reference to another post or website would be much appreciated.