feat: support extending McpServer with subclass

src/shared/protocol.ts

@@ -93,6 +93,11 @@ export type RequestHandlerExtra = {
    * The session ID from the transport, if available.
    */
   sessionId?: string;
+
+  /**
+   * The authenticated user, if available.
+   */
+  user?: unknown;
 };
 
 /**
@@ -316,6 +321,7 @@ export abstract class Protocol<
     const extra: RequestHandlerExtra = {
       signal: abortController.signal,
       sessionId: this._transport?.sessionId,
+      user: this._transport?.user,
     };
 
     // Starting with Promise.resolve() puts any synchronous errors into the monad as well.
@@ -361,7 +367,7 @@ export abstract class Protocol<
   private _onprogress(notification: ProgressNotification): void {
     const { progressToken, ...params } = notification.params;
     const messageId = Number(progressToken);
-    
+
     const handler = this._progressHandlers.get(messageId);
     if (!handler) {
       this._onerror(new Error(`Received a progress notification for an unknown token: ${JSON.stringify(notification)}`));

src/shared/transport.ts

@@ -46,4 +46,9 @@ export interface Transport {
    * The session ID generated for this connection.
    */
   sessionId?: string;
+
+  /**
+   * The authenticated user for this transport session.
+   */
+  user?: unknown;
 }