Note: Since 2021, I strongly recommend to use git credential manager core instead of using this older method. See How to install git credential manager core on Ubuntu 20.04
Problem:
Every time you clone a git repository or push/pull, you have to enter a username and a password (e.g. for GitHub or your GitLab installation).
Instead, you want git to store the password so you only have to enter it once.
Solution:
Configure the git credential helper to use a plaintext store instead of the default cache:
git config --global credential.helper store
NOTE: This approach will store your passwords in a plaintext file, so depending on your setup this might be a security risk.