Authentication failure on brew tap with private repository

Homebrew installs to a user-owned prefix and avoids root for most operations. The Tap mechanism clones remote repositories using the local Git installation, so authentication for private taps is delegated to the system's Git credential helper rather than being managed internally by Homebrew.

Least-privilege operation means tap operations should not require elevated privileges, but credential handling depends on the Git configuration in place for the user. When credentials expire, the interaction between Homebrew's user-space execution and Git's authentication prompts is not fully documented.

Clarification is needed on the expected failure mode and consistency across environments.

Does Homebrew surface Git authentication errors directly during a tap operation? Is credential prompting behavior consistent when the system Git credential helper is configured for least-privilege access? How are expired SSH keys or tokens handled without privilege escalation?