NestJS Enterprise Backend APIs · レッスン

Socket接続の認証と保護

安全なリアルタイムアクセスのため、handshakeとmessage eventにguardとトークン検証を適用します

「Socket接続の認証と保護」はCoddyKit上の無料NestJS Enterprise Backend APIsレッスンです。これはレッスン2/4です。下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。これはNestJS Enterprise Backend APIs学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 NestJS Enterprise Backend APIsコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Why Sockets Need Their Own Auth Story

HTTP routes in NestJS are protected by middleware and guards that read the Authorization header on every request. WebSockets are different: the client opens one long-lived connection during the handshake, then exchanges many messages over it.

You authenticate once at connection time, not per message.
The socket stays open for minutes or hours, so a token that expires mid-session is a real concern.
Standard HTTP guards do not automatically run on WebSocket events.

This lesson shows how to verify a token during the handshake, attach the user to the socket, and guard individual message events for secure realtime access.

Where the Token Lives in a Handshake

A browser WebSocket cannot set custom headers, so clients pass the token in one of three places during the Socket.IO handshake:

handshake.auth.token — the modern, preferred slot (set via the client auth option).
handshake.headers.authorization — works when a native header is available.
handshake.query.token — a fallback, but tokens land in server/proxy logs, so avoid it.

A small helper centralizes extraction so every guard and lifecycle hook reads the token the same way.

import { Socket } from 'socket.io';

export function extractToken(client: Socket): string | null {
  const auth = client.handshake.auth?.token;
  if (typeof auth === 'string') return auth;

  const header = client.handshake.headers?.authorization;
  if (typeof header === 'string' && header.startsWith('Bearer ')) {
    return header.slice(7);
  }

  return null;
}

Verifying on Connection with handleConnection

The cleanest place to authenticate is the gateway's handleConnection lifecycle hook. It runs the moment a client connects. If the token is missing or invalid, call client.disconnect() so the socket never participates in any room or event.

On success, attach the decoded user to client.data — a per-socket bag that survives for the connection's lifetime and is readable in every later event handler.

import { OnGatewayConnection, WebSocketGateway } from '@nestjs/websockets';
import { JwtService } from '@nestjs/jwt';
import { Socket } from 'socket.io';
import { extractToken } from './extract-token';

@WebSocketGateway({ cors: true })
export class ChatGateway implements OnGatewayConnection {
  constructor(private readonly jwt: JwtService) {}

  async handleConnection(client: Socket) {
    try {
      const token = extractToken(client);
      if (!token) throw new Error('No token');
      const payload = await this.jwt.verifyAsync(token);
      client.data.user = { id: payload.sub, role: payload.role };
    } catch {
      client.disconnect(true);
    }
  }
}

Modeling the Authenticated User

Storing client.data.user as an untyped object invites typos later. Define a small interface and a typed helper so every handler reads user.id and user.role with full IntelliSense and compile-time safety.

This is the same JWT payload pattern you use for HTTP routes, keeping authorization logic consistent across both transports.

export interface SocketUser {
  id: string;
  role: 'admin' | 'member' | 'guest';
}

export interface JwtPayload {
  sub: string;
  role: SocketUser['role'];
  exp: number;
}

export function toSocketUser(payload: JwtPayload): SocketUser {
  return { id: payload.sub, role: payload.role };
}

// Demo: a decoded token becomes a typed user
const payload: JwtPayload = { sub: 'u_42', role: 'member', exp: 1893456000 };
const user = toSocketUser(payload);
console.log(`${user.id} connected as ${user.role}`);

Guarding Individual Message Events

Connection-time auth proves who the user is, but some events also need authorization checks — for example, only admins can broadcast a system message. NestJS guards work on WebSocket events too; you just read the socket from the execution context.

Inside a guard, switch the context to ws, grab the client, and inspect client.data.user that handleConnection populated.

import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
import { WsException } from '@nestjs/websockets';
import { Socket } from 'socket.io';

@Injectable()
export class WsAuthGuard implements CanActivate {
  canActivate(context: ExecutionContext): boolean {
    const client = context.switchToWs().getClient<Socket>();
    const user = client.data.user;
    if (!user) {
      throw new WsException('Unauthorized');
    }
    return true;
  }
}

Role-Based Guards with Metadata

To restrict an event to certain roles, combine a custom decorator (storing required roles as metadata) with a guard that reads it via Reflector. This mirrors the HTTP @Roles() pattern, so your team learns one mental model.

The guard rejects the event with a WsException when the connected user lacks the required role — the message handler never runs.

import { SetMetadata } from '@nestjs/common';
export const WsRoles = (...roles: string[]) => SetMetadata('ws_roles', roles);

import { CanActivate, ExecutionContext, Injectable } from '@nestjs/common';
import { Reflector } from '@nestjs/core';
import { WsException } from '@nestjs/websockets';
import { Socket } from 'socket.io';

@Injectable()
export class WsRolesGuard implements CanActivate {
  constructor(private reflector: Reflector) {}

  canActivate(context: ExecutionContext): boolean {
    const required = this.reflector.get<string[]>('ws_roles', context.getHandler());
    if (!required?.length) return true;
    const user = context.switchToWs().getClient<Socket>().data.user;
    if (!user || !required.includes(user.role)) {
      throw new WsException('Forbidden');
    }
    return true;
  }
}

Applying Guards to Subscribe Handlers

Attach guards to message handlers with @UseGuards(), exactly like controller routes. Stack the base auth guard with the roles guard, and decorate the handler with the required roles.

Guards run in declaration order, so put the cheaper authentication check first and the role check second.

import { SubscribeMessage, WebSocketGateway, MessageBody } from '@nestjs/websockets';
import { UseGuards } from '@nestjs/common';
import { WsAuthGuard } from './ws-auth.guard';
import { WsRolesGuard } from './ws-roles.guard';
import { WsRoles } from './ws-roles.decorator';

@WebSocketGateway()
export class AdminGateway {
  @UseGuards(WsAuthGuard, WsRolesGuard)
  @WsRoles('admin')
  @SubscribeMessage('broadcast')
  handleBroadcast(@MessageBody() text: string) {
    return { event: 'broadcast', data: text };
  }
}

Why Guards Alone Miss the Handshake

A subtle gotcha: by default a WebSocket guard runs on message events, not on the initial connection. If you rely only on @UseGuards and skip handleConnection, an unauthenticated client can still open a socket and sit idle in your server.

Use handleConnection to reject unauthenticated sockets at the door.
Use event guards for fine-grained, per-action authorization.

The two layers complement each other: one controls entry, the other controls actions.

Surfacing Errors Cleanly to Clients

When a guard throws WsException, NestJS emits an exception event to that client instead of crashing the connection. Add a WsExceptionFilter to shape the payload so the frontend gets a predictable error object it can show to the user.

import { ArgumentsHost, Catch } from '@nestjs/common';
import { BaseWsExceptionFilter, WsException } from '@nestjs/websockets';
import { Socket } from 'socket.io';

@Catch(WsException)
export class WsErrorFilter extends BaseWsExceptionFilter {
  catch(exception: WsException, host: ArgumentsHost) {
    const client = host.switchToWs().getClient<Socket>();
    client.emit('error', {
      message: exception.getError(),
      timestamp: new Date().toISOString(),
    });
  }
}

Handling Token Expiry on a Live Socket

A connection authenticated an hour ago may now hold an expired token. Two common strategies:

Re-verify per sensitive event — store the raw token on client.data.token and call verifyAsync again inside the guard for high-value actions.
Periodic revalidation — a server interval checks each socket's token exp and disconnects expired ones.

This small pure function shows the expiry check at the heart of either approach.

interface TokenInfo {
  exp: number; // unix seconds
}

function isExpired(token: TokenInfo, nowSeconds: number): boolean {
  return token.exp <= nowSeconds;
}

const now = 1_700_000_000;
console.log(isExpired({ exp: 1_699_999_000 }, now)); // true  -> disconnect
console.log(isExpired({ exp: 1_700_500_000 }, now)); // false -> keep open

Wiring It Together in the Module

Guards that inject services like Reflector or JwtService must be resolvable by Nest's DI. Because the gateway and its guards live in the same module, register JwtModule and provide the gateway; the guards are instantiated by Nest when referenced in @UseGuards.

You can also register the auth guard globally for sockets with APP_GUARD if every event should be authenticated by default.

import { Module } from '@nestjs/common';
import { JwtModule } from '@nestjs/jwt';
import { APP_GUARD } from '@nestjs/core';
import { ChatGateway } from './chat.gateway';
import { WsAuthGuard } from './ws-auth.guard';

@Module({
  imports: [
    JwtModule.register({ secret: process.env.JWT_SECRET }),
  ],
  providers: [
    ChatGateway,
    { provide: APP_GUARD, useClass: WsAuthGuard },
  ],
})
export class RealtimeModule {}

Quick Check: Connection vs Event Auth

You want to (1) block unauthenticated clients from ever opening a socket and (2) allow only admin users to emit a broadcast event. Which combination correctly achieves both?

Recap: Securing Realtime Connections

You now have a complete, layered approach to securing NestJS WebSocket gateways:

Extract the token consistently from handshake.auth, headers, or query.
Authenticate at the door in handleConnection, disconnecting invalid clients and attaching the user to client.data.
Authorize per event with guards that switch to the ws context, including role checks via Reflector and a @WsRoles decorator.
Report errors through a WsException filter, and handle expiry with re-verification or periodic checks.

Connection auth controls entry; event guards control actions — together they keep your realtime system secure.

よくある質問

「Socket接続の認証と保護」レッスンは無料ですか？

はい。「Socket接続の認証と保護」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、NestJS Enterprise Backend APIsコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 NestJS Enterprise Backend APIsコースには全4レッスンが含まれています。

「Socket接続の認証と保護」で何を学びますか？

安全なリアルタイムアクセスのため、handshakeとmessage eventにguardとトークン検証を適用しますブラウザで直接実行するハンズオンコードでNestJS Enterprise Backend APIsを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

NestJS Enterprise Backend APIsを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのNestJS Enterprise Backend APIsは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。これはレッスン2/4です。

「Socket接続の認証と保護」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このNestJS Enterprise Backend APIsレッスンでコードを書いて実行できますか？

はい。すべてのNestJS Enterprise Backend APIsレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

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