Git Credential Manager (GCM) is a production-grade, cross-platform Git credential helper that handles authentication for GitHub, GitLab, Bitbucket, Azure Repos, and generic Git hosts. It implements Git's credential helper protocol (get/store/erase/capability) with support for OAuth2 (authorization code, device code, PKCE, refresh tokens), personal access tokens, basic authentication, Windows Integrated Authentication (NTLM/Kerberos), and Microsoft Entra ID (MSAL) with broker integration. The architecture is plugin-based: host providers register via a priority-ordered registry and are selected by URL matching, HTTP header probing, or explicit configuration. Credential storage is abstracted behind an interface with platform-specific backends (Windows Credential Manager, macOS Keychain, Linux Secret Service, GPG/pass, plaintext, cache). Interactive prompts are delivered via a terminal UI (Spectre.Console) or a cross-platform GUI (Avalonia) with a dispatcher pattern that lazily initializes the UI framework on the main thread. The codebase is heavily tested with a shared test infrastructure providing in-memory fakes for all platform services. Key entry points include Program.cs (process entry), Application.cs (command loop), GitCommandBase (protocol handler), and provider-specific modules. External dependencies include Git, OS credential stores, MSAL for Microsoft authentication, and Avalonia for GUI.