fix(mcp): Display OAuth authentication messages in CLI UI instead of debug console (#6919)

Co-authored-by: Yoichiro Tanaka <yoichiro6642@gmail.com>
Co-authored-by: Jacob Richman <jacob314@gmail.com>

packages/cli/src/ui/commands/mcpCommand.test.ts

@@ -904,6 +904,7 @@ describe('mcpCommand', () => {
         'test-server',
         { enabled: true },
         'http://localhost:3000',
+        expect.any(Object),
       );
       expect(mockToolRegistry.discoverToolsForServer).toHaveBeenCalledWith(
         'test-server',

packages/cli/src/ui/commands/mcpCommand.ts

@@ -22,6 +22,7 @@ import {
   getErrorMessage,
   MCPOAuthTokenStorage,
 } from '@google/gemini-cli-core';
+import { appEvents, AppEvent } from '../../utils/events.js';
 
 const COLOR_GREEN = '\u001b[32m';
 const COLOR_YELLOW = '\u001b[33m';
@@ -368,6 +369,12 @@ const authCommand: SlashCommand = {
     // Always attempt OAuth authentication, even if not explicitly configured
     // The authentication process will discover OAuth requirements automatically
 
+    const displayListener = (message: string) => {
+      context.ui.addItem({ type: 'info', text: message }, Date.now());
+    };
+
+    appEvents.on(AppEvent.OauthDisplayMessage, displayListener);
+
     try {
       context.ui.addItem(
         {
@@ -385,10 +392,14 @@ const authCommand: SlashCommand = {
         oauthConfig = { enabled: false };
       }
 
-      // Pass the MCP server URL for OAuth discovery
       const mcpServerUrl = server.httpUrl || server.url;
       const authProvider = new MCPOAuthProvider(new MCPOAuthTokenStorage());
-      await authProvider.authenticate(serverName, oauthConfig, mcpServerUrl);
+      await authProvider.authenticate(
+        serverName,
+        oauthConfig,
+        mcpServerUrl,
+        appEvents,
+      );
 
       context.ui.addItem(
         {
@@ -430,6 +441,8 @@ const authCommand: SlashCommand = {
         messageType: 'error',
         content: `Failed to authenticate with MCP server '${serverName}': ${getErrorMessage(error)}`,
       };
+    } finally {
+      appEvents.removeListener(AppEvent.OauthDisplayMessage, displayListener);
     }
   },
   completion: async (context: CommandContext, partialArg: string) => {

packages/cli/src/utils/events.ts

@@ -9,6 +9,7 @@ import { EventEmitter } from 'node:events';
 export enum AppEvent {
   OpenDebugConsole = 'open-debug-console',
   LogError = 'log-error',
+  OauthDisplayMessage = 'oauth-display-message',
 }
 
 export const appEvents = new EventEmitter();