fatal: Authentication failed for 'https://github.com/user/repo.git'

Workarounds

1. 94% success Generate a personal access token (PAT) and use it instead of a password

   # GitHub: Settings > Developer Settings > Personal Access Tokens > Generate new token
   # Use the token as the password when git prompts for credentials.
   # Store it so you don't have to re-enter:
   git config --global credential.helper store

   Sources: https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token

2. 90% success For SSH, test key with ssh -T and add to agent if needed

   # Test SSH connectivity:
   ssh -T [email protected]
   
   # If key not found, add it to the agent:
   eval $(ssh-agent -s)
   ssh-add ~/.ssh/id_ed25519
   
   # If no key exists, generate one:
   ssh-keygen -t ed25519 -C '[email protected]'
   # Then add the public key to GitHub/GitLab settings.

   Sources: https://docs.github.com/en/authentication/connecting-to-github-with-ssh/testing-your-ssh-connection

3. 88% success Use credential helper to cache or store credentials securely

   # Cache credentials in memory for 1 hour:
   git config --global credential.helper 'cache --timeout=3600'
   
   # Store credentials on disk (less secure):
   git config --global credential.helper store
   
   # On macOS, use Keychain:
   git config --global credential.helper osxkeychain
   
   # On Linux, use libsecret:
   git config --global credential.helper /usr/libexec/git-core/git-credential-libsecret

   Sources: https://git-scm.com/docs/gitcredentials