Working with PassportJS

Detailed documentation on working with PassportJS library

Passport is the most popular node.js authentication library, well-known by the community and successfully used in many production applications. It's straightforward to integrate this library with a Nest application using the @nestjs/passport module

Steps to Use Passport in NestJS

1. Install Dependencies You'll need to install @nestjs/passport, passport, and any specific Passport strategies you want to use (e.g., passport-jwt, passport-facebook, etc.).

   yarn add @nestjs/passport passport passport-jwt

2. Create the Strategy A Passport strategy in NestJS is typically implemented as an injectable service by extending the PassportStrategy class from @nestjs/passport. You use this class to implement the required strategy.

   Example: Facebook Strategy for OAuth Authentication

   import { Injectable, UnauthorizedException } from '@nestjs/common';
   import { PassportStrategy } from '@nestjs/passport';
   import { Strategy, ExtractJwt } from 'passport-jwt';
   import { JwtUserPayload } from 'src/common/interfaces/jwt-user-payload.interface';
   import constants from 'src/constants';
   
   @Injectable()
   export class JwtStrategy extends PassportStrategy(Strategy, 'jwt') {
       constructor() {
           super({
               jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
               secretOrKey: constants.TOKEN_SECRET,
           });
       }
   
       async validate(payload: JwtUserPayload): Promise<JwtUserPayload> {
           if (!payload) {
               throw new UnauthorizedException();
           }
           return payload;
       }
   }

   Here, validate is called when the strategy is triggered, and you check the credentials.

3. Register the Strategy In your Auth Module, you register the strategy as a provider so that it can be injected and used.

   import { Module } from '@nestjs/common';
   import { PassportModule } from '@nestjs/passport';
   import { AuthService } from './auth.service';
   import { JwtStrategy } from './jwt-strategy';
   
   @Module({
     imports: [PassportModule],
     providers: [AuthService, JwtStrategy],
   })
   export class AuthModule {}

4. Use the Strategy in a Guard, you apply Passport strategies using guards. NestJS has a built-in AuthGuard that integrates with Passport.

   Example: Facebook Auth Guard

   import { Injectable } from '@nestjs/common';
   import { AuthGuard } from '@nestjs/passport';
   
   @Injectable()
   export class JwtAuthenticationGuard extends AuthGuard('jwt') {}

   The string 'jwt' refers to the strategy defined in the FacebookStrategy class.

5. Use the Guard in a Controller Now, you can apply the guard to a route in your controller to protect it using the Passport strategy.

   Example: Using the JwtAuthGuard in a Controller

   typescriptCopy codeimport { Controller, Post, UseGuards, Request } from '@nestjs/common';
   import { AuthService } from './auth.service';
   import { LocalAuthGuard } from './local-auth.guard';
   
   @Controller('auth')
   export class AuthController {
     constructor(private authService: AuthService) {}
   
     @UseGuards(JwtAuthenticationGuard)
       @Post('change-team')
       async changeTeam(@Body('teamId') teamId: string, @GetUser() user: JwtUserPayload) {
           return await this.authService.changeTeam(user, teamId);
       }
   }

   In this case JwtAuthenticationGuard will returns us Authenticated user data.

Key Components:

1. Strategy: Implements a specific authentication mechanism.

2. Guard: Applies the strategy to route handlers to protect them.

By using Passport strategies in NestJS, you can easily implement complex authentication mechanisms (like JWT, OAuth, etc.) in a modular and structured way.

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