Is it best to declare global variables in a header file or environment file in a C project

Question

I want to know about best practices with C, in creating a API connection wrapper, I have credentials and a variety of non-security related global variables. This will be in a public git repository so I don't want to expose sensitive data. However, I need the security data at compile time, not just at runtime. I see the git ignore file templates on github, but am not sure where to start. What is the process to organizing globals in a secure way?

The example directory includes:

Project
 -data
 -src
  -main.c
  -header.c
  -header.h
 -env
  -credentials.env
 Makefile