FastMCP changed in mcp 2.3.0

Verified example for mcp 2.3.0

import asyncio

import anyio

from mcp import ClientSession
from mcp.server.auth.middleware.auth_context import get_access_token
from mcp.server.mcpserver import Context, MCPServer
from mcp.shared.memory import create_client_server_memory_streams

mcp = MCPServer("whoami-server")


@mcp.tool()
def whoami(ctx: Context) -> str:
    """Return the client ID from the request context, or 'anonymous'."""
    access_token = get_access_token()
    client_id = access_token.client_id if access_token else None
    return client_id if client_id else "anonymous"


async def main() -> None:
    # MCPServer wraps a low-level server.
    # Create in-memory streams, run the server on them and an initialized ClientSession.
    server = getattr(mcp, "_lowlevel_server", None) or mcp._mcp_server
    async with create_client_server_memory_streams() as (client_streams, server_streams):
        async with anyio.create_task_group() as tg:
            tg.start_soon(
                server.run,
                server_streams[0],
                server_streams[1],
                server.create_initialization_options(),
            )
            async with ClientSession(client_streams[0], client_streams[1]) as client:
                await client.initialize()
                result = await client.call_tool("whoami", {})
                for item in result.content:
                    text = getattr(item, "text", None)
                    if text is not None:
                        print(text)
            tg.cancel_scope.cancel()


if __name__ == "__main__":
    asyncio.run(main())