Complete Git Authentication Troubleshooting Guide

A user experienced a Git pull failure, receiving a "Repository not found" error. The issue stemmed from using an outdated email address linked to their previous GitHub account. Initial troubleshooting involved verifying Git configuration and SSH connection, but these steps failed to resolve the problem. Switching to HTTPS authentication proved to be the key solution. The user updated the remote repository URL to HTTPS and successfully pulled the changes. However, a "refusing to merge unrelated histories" error appeared, necessitating a forced merge using the `--allow-unrelated-histories` flag. The core solutions addressed authentication method selection (SSH vs. HTTPS), credential management (using Personal Access Tokens), and handling unrelated repository histories. Preventive measures include regularly updating Git configurations, choosing appropriate authentication methods, and backing up important settings. Common variant problems included permission denied errors and authentication failures, each with specific solutions. The final solution involved using HTTPS, forcing a merge of unrelated histories, and configuring the pull strategy. The document offers troubleshooting commands, best practices, and additional resources for resolving similar Git authentication issues. This comprehensive guide aids in resolving Git authentication problems across different operating systems.