using GIT_ASKPASS to set credentials

`GIT_ASKPASS` is an environment variable that can be used to set credentials for Git operations that require authentication. It specifies a script to be used by Git to prompt for a username and password. The script should output the credentials to stdout in the format `username:password`.

For example, to set the `GIT_ASKPASS` variable to prompt for credentials using a script named `git-askpass.sh`, you would run:

export GIT_ASKPASS=/path/to/git-askpass.sh

Then, when Git needs to authenticate, it will execute the script and use the credentials output by the script.

Note that the exact implementation of `GIT_ASKPASS` may vary depending on your operating system and Git version.