When you are using third-party sources for app development, there is a need for the involvement of SSH keys or API credentials. This goes on to become a problem when it is handled by a team of developers. Thus, the source code has to be pushed to Git repositories periodically. Once the code is pushed to a repository, anyone can see it with third-party keys.
A very prominent and widely used solution for this problem is using environment variables. These are the local variables containing some useful information like API keys and are made available to the application or project.