No client secrets ever touch the AI agent. The agent's browser proves possession of the auth code via a cryptographic verifier. This is what Claude, every CLI agent, and most modern AI clients use by default. It's the OAuth 2.1 standard for public clients — the safest available option for software that runs on someone else's machine.
Anthropic Claude
Claude.ai and Claude Desktop call MCP servers Custom Connectors. Claude Code (the CLI) just calls them MCP servers. Same underlying protocol, two different labels in the UI.