Copilot is an agent / MCP client, to makes calls to both LLMs and various MCP servers.
In the very first MCP version Antropic suggested each MCP server should both be an
OAuth "authentication provider" (AP) and a "resource provider" (RP) but this makes each
MCP server really complex/bloated/weird.
.well-known/oauth-protected-resource
A2A = Google Agent-to-Agent protocol
MCP = Model Context Protocol