Build SMS OTP Two-Factor Authentication with Sinch and Fastify

+-------------+       +-----------------+      +-----------------+      +-----------------+
| End User    | <---> | Frontend App    | <--> | Fastify Backend | <--> | Sinch Platform  |
| (Browser/   |       | (React/Vue/etc.)|      | (Node.js/TS)    |      | (Verification   |
| Mobile App) |       +-----------------+      +-------+---------+      | API via SDK)    |
+-------------+                                        |                +-----------------+
                                                       |
                                               +-------+---------+
                                               | Database        |
                                               | (PostgreSQL/    |
                                               |  Prisma)        |
                                               +-----------------+

# Create project directory and navigate into it
mkdir fastify-sinch-otp
cd fastify-sinch-otp

# Initialize Node.js project
npm init -y

# Install Fastify and core dependencies (Fastify v5 current as of 2025)
npm install fastify @fastify/sensible

# Install TypeScript and related development dependencies
npm install --save-dev typescript @types/node ts-node nodemon @tsconfig/node20

# Install Prisma (ORM) and PostgreSQL driver
npm install @prisma/client
npm install --save-dev prisma pg # pg is the Node.js driver for PostgreSQL

# Install Sinch Verification SDK
npm install @sinch/verification

# Install libraries for environment variables and validation
npm install dotenv fastify-type-provider-zod zod

# Install libraries for JWT authentication and password hashing
npm install @fastify/jwt bcrypt
npm install --save-dev @types/bcrypt @types/jsonwebtoken # @types/jsonwebtoken might be implicitly handled by @fastify/jwt, but explicit install is safe.

// tsconfig.json
{
  "extends": "@tsconfig/node20/tsconfig.json",
  "compilerOptions": {
    "outDir": "dist",
    "rootDir": "src",
    "module": "CommonJS",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true,
    "sourceMap": true,
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules", "**/*.spec.ts"]
}

// package.json (add or modify the "scripts" section)
"scripts": {
  "build": "tsc",
  "start": "node dist/server.js",
  "dev": "nodemon --watch src --ext ts --exec ts-node src/server.ts",
  "test": "vitest run", // Example using Vitest; replace with your test runner command (e.g., "jest")
  "prisma:dev:deploy": "prisma migrate deploy",
  "prisma:dev:migrate": "prisma migrate dev",
  "prisma:generate": "prisma generate",
  "prisma:studio": "prisma studio"
},

# .env.example

# Application Configuration
NODE_ENV=development
PORT=3000
HOST=0.0.0.0 # Listen on all available network interfaces

# Database Configuration (PostgreSQL example)
DATABASE_URL="postgresql://user:password@localhost:5432/mydatabase?schema=public"

# Sinch Configuration
# Get these from your Sinch Dashboard -> Verification -> Your App
SINCH_APPLICATION_KEY=YOUR_SINCH_APP_KEY
SINCH_APPLICATION_SECRET=YOUR_SINCH_APP_SECRET

# JWT Configuration
JWT_SECRET=a_very_strong_and_long_secret_key_please_change_me # Use a secure random string
JWT_EXPIRES_IN=1h # How long a standard login token lasts
JWT_OTP_EXPIRES_IN=5m # How long a temporary pre-OTP token lasts

# .gitignore
node_modules
dist
.env
npm-debug.log*
yarn-debug.log*
yarn-error.log*

# docker-compose.yml
version: '3.8'
services:
  postgres:
    image: postgres:15
    container_name: fastify_sinch_db
    restart: always
    ports:
      - "5432:5432" # Expose port 5432 locally
    environment:
      POSTGRES_USER: user        # Match your .env DATABASE_URL
      POSTGRES_PASSWORD: password # Match your .env DATABASE_URL
      POSTGRES_DB: mydatabase   # Match your .env DATABASE_URL
    volumes:
      - postgres_data:/var/lib/postgresql/data

volumes:
  postgres_data:

// prisma/schema.prisma

generator client {
  provider = "prisma-client-js"
}

datasource db {
  provider = "postgresql"
  url      = env("DATABASE_URL") // Loads from .env file
}

model User {
  id        String   @id @default(cuid()) // Unique identifier
  email     String   @unique             // User's email, must be unique
  password  String                       // Hashed password
  name      String?                      // Optional user name
  phone     String?  @unique             // User's phone number, unique if present
                                         // Make required if needed for your flow

  // Timestamps
  createdAt DateTime @default(now())
  updatedAt DateTime @updatedAt
}

// You could add more models here (e.g., Session, AuditLog) if needed

// src/plugins/prisma.ts
import fp from 'fastify-plugin';
import { PrismaClient } from '@prisma/client';

declare module 'fastify' {
  interface FastifyInstance {
    prisma: PrismaClient;
  }
}

export default fp(async (fastify) => {
  const prisma = new PrismaClient();

  await prisma.$connect(); // Connect to the database when the plugin is loaded

  // Make Prisma Client available through the fastify instance: fastify.prisma
  fastify.decorate('prisma', prisma);

  // Add a hook to disconnect Prisma Client when the server shuts down
  fastify.addHook('onClose', async (instance) => {
    await instance.prisma.$disconnect();
  });
});

// src/config/index.ts
import dotenv from 'dotenv';
import { z } from 'zod';

dotenv.config(); // Load .env file

const envSchema = z.object({
  NODE_ENV: z.enum(['development', 'production', 'test']).default('development'),
  PORT: z.coerce.number().default(3000),
  HOST: z.string().default('0.0.0.0'),
  DATABASE_URL: z.string().url(),
  SINCH_APPLICATION_KEY: z.string().min(1, "Sinch Application Key is required"),
  SINCH_APPLICATION_SECRET: z.string().min(1, "Sinch Application Secret is required"),
  JWT_SECRET: z.string().min(64, "JWT Secret must be at least 64 characters long per OWASP recommendations"),
  JWT_EXPIRES_IN: z.string().default('30m'), // Per OWASP: 15-30 min idle timeout
  JWT_OTP_EXPIRES_IN: z.string().default('5m'),
});

// Validate environment variables at startup
try {
  const config = envSchema.parse(process.env);
  console.log("_ Environment variables loaded successfully.");

  // Make config available globally (or export selectively)
  // Option 1: Simple export
  // export default config;

  // Option 2: More structured export (if needed)
  const appConfig = {
      env: config.NODE_ENV,
      port: config.PORT,
      host: config.HOST,
      databaseUrl: config.DATABASE_URL,
      sinch: {
          appKey: config.SINCH_APPLICATION_KEY,
          appSecret: config.SINCH_APPLICATION_SECRET,
      },
      jwt: {
          secret: config.JWT_SECRET,
          expiresIn: config.JWT_EXPIRES_IN,
          otpExpiresIn: config.JWT_OTP_EXPIRES_IN,
      }
  };
  console.log("__  App Config:", { // Log non-sensitive parts
    env: appConfig.env,
    port: appConfig.port,
    host: appConfig.host,
    jwt: { expiresIn: appConfig.jwt.expiresIn, otpExpiresIn: appConfig.jwt.otpExpiresIn }
  });
  // Export the structured config
  // (Remove sensitive details like full DB URL, secrets from logs in production)
  if (appConfig.env !== 'development') {
      console.log("__ Sinch App Key: [Loaded]"); // Avoid logging keys in prod
  } else {
      console.log(`__ Sinch App Key: ${appConfig.sinch.appKey.substring(0, 5)}...`);
  }
  export default appConfig;


} catch (error) {
  if (error instanceof z.ZodError) {
    console.error("_ Invalid environment variables:", error.format());
  } else {
    console.error("_ Error loading environment variables:", error);
  }
  process.exit(1); // Exit if config is invalid
}

// src/modules/auth/auth.schema.ts
import { z } from 'zod';

// --- Input Schemas ---

// Schema for user registration input
export const registerUserSchema = z.object({
  email: z.string().email({ message: "Invalid email address" }),
  password: z.string().min(8, { message: "Password must be at least 8 characters long" }),
  name: z.string().optional(),
  phone: z.string().min(10, { message: "Phone number seems too short" })
             .max(15, { message: "Phone number seems too long"})
             .regex(/^\+?[1-9]\d{1,14}$/, { message: "Invalid phone number format (E.164 expected: +[country code][number], max 15 digits total, e.g., +14155552671)"}), // E.164 format per ITU-T standard
});
export type RegisterUserInput = z.infer<typeof registerUserSchema>;

// Schema for user login input
export const loginUserSchema = z.object({
  email: z.string().email(),
  password: z.string(),
});
export type LoginUserInput = z.infer<typeof loginUserSchema>;

// Schema for initiating OTP
export const initiateOtpSchema = z.object({
    // Typically, the phone number comes from the logged-in user's profile (via JWT)
    // If allowing arbitrary numbers, add validation here:
    // phone: z.string().min(10).max(15).regex(/^\+?[1-9]\d{1,14}$/),
});
export type InitiateOtpInput = z.infer<typeof initiateOtpSchema>; // May not be needed if using user context


// Schema for verifying OTP
export const verifyOtpSchema = z.object({
  otp: z.string().length(4, { message: "OTP must be 4 digits" }) // Adjust length based on Sinch config (default 4-6 digits)
           .regex(/^\d+$/, { message: "OTP must contain only digits" }),
});
export type VerifyOtpInput = z.infer<typeof verifyOtpSchema>;

// --- Response Schemas (Examples) ---

export const authResponseSchema = z.object({
    accessToken: z.string()
});

export const userResponseSchema = z.object({
    id: z.string(),
    email: z.string(),
    name: z.string().nullable(),
    phone: z.string().nullable(),
    createdAt: z.date(),
});

export const loginResponseSchema = z.object({
    otpToken: z.string().optional(),
    accessToken: z.string().optional(),
    message: z.string().optional()
});

export const messageResponseSchema = z.object({
    message: z.string()
});


// --- JWT Payload Types ---

export interface AuthJWTPayload {
  id: string;
  email: string;
  otpVerified: boolean; // Flag to track OTP status
}

export interface OtpJWTPayload {
    id: string;
    phone: string; // Include phone needed for OTP verification
}

// src/utils/hash.ts
import bcrypt from 'bcrypt';

const SALT_ROUNDS = 12; // Per OWASP 2024-2025 recommendations (minimum 10, recommended 12-14 for balance of security and performance)

export async function hashPassword(password: string): Promise<string> {
  return bcrypt.hash(password, SALT_ROUNDS);
}

export async function comparePassword(plain: string, hash: string): Promise<boolean> {
  return bcrypt.compare(plain, hash);
}

// src/modules/auth/auth.service.ts
import { PrismaClient, User } from '@prisma/client';
import { hashPassword, comparePassword } from '../../utils/hash';
import { RegisterUserInput, LoginUserInput } from './auth.schema';
import { BadRequest, NotFound, Unauthorized } from 'http-errors'; // Use http-errors for standard HTTP errors

export class AuthService {
  constructor(private prisma: PrismaClient) {} // Inject Prisma client

  async registerUser(input: RegisterUserInput): Promise<Omit<User_ 'password'>> {
    const { email, password, name, phone } = input;

    // Check if user or phone already exists
    const existingUser = await this.prisma.user.findFirst({
      where: { OR: [{ email }, { phone }] }, // Check uniqueness for both email and phone
    });

    if (existingUser) {
        if (existingUser.email === email) {
            throw new BadRequest('User with this email already exists.');
        }
        if (existingUser.phone === phone) {
             throw new BadRequest('User with this phone number already exists.');
        }
    }

    const hashedPassword = await hashPassword(password);

    const user = await this.prisma.user.create({
      data: {
        email,
        password: hashedPassword,
        name,
        phone,
      },
    });

    // eslint-disable-next-line @typescript-eslint/no-unused-vars
    const { password: _, ...userWithoutPassword } = user; // Exclude password from return
    return userWithoutPassword;
  }

  async loginUser(input: LoginUserInput): Promise<User&gt; {
    const { email, password } = input;

    const user = await this.prisma.user.findUnique({
      where: { email },
    });

    if (!user) {
      throw new NotFound('User not found.'); // More specific than Unauthorized before checking password
    }

    const isPasswordValid = await comparePassword(password, user.password);

    if (!isPasswordValid) {
      throw new Unauthorized('Invalid password.');
    }

    // User is found and password is valid
    return user;
  }

  // Find user by ID (useful for getting user details after JWT validation)
  async findUserById(userId: string): Promise<Omit<User_ 'password'&gt; | null&gt; {
    const user = await this.prisma.user.findUnique({
        where: { id: userId },
        select: { // Explicitly select fields to exclude password
            id: true,
            email: true,
            name: true,
            phone: true,
            createdAt: true,
            updatedAt: true,
        }
    });
    if (!user) {
        throw new NotFound('User not found.');
    }
    return user;
  }

}

// src/modules/auth/auth.controller.ts
import { FastifyRequest, FastifyReply, FastifyInstance } from 'fastify';
import { AuthService } from './auth.service';
import {
    RegisterUserInput,
    LoginUserInput,
    VerifyOtpInput,
    AuthJWTPayload, // Import JWT types
    OtpJWTPayload   // Import JWT types
} from './auth.schema';
import config from '../../config'; // Import app config
import { BadRequest, Unauthorized } from 'http-errors'; // Import error types

export class AuthController {
  constructor(
      private authService: AuthService,
      private fastify: FastifyInstance // Need fastify instance for JWT signing
    ) {}

  async registerHandler(request: FastifyRequest<{ Body: RegisterUserInput }>, reply: FastifyReply) {
    try {
      const user = await this.authService.registerUser(request.body);
      // Decide on registration flow:
      // 1. Log in directly?
      // 2. Require email verification?
      // 3. Require OTP verification immediately?
      // For this guide, we'll return the user data (excluding password)
      // and require them to log in separately to start the OTP flow.
      return reply.code(201).send(user);
    } catch (error: any) {
        request.log.error(error, "Registration failed");
        // Let the global error handler (added later) handle http-errors
        throw error;
    }
  }

  async loginHandler(request: FastifyRequest<{ Body: LoginUserInput }>, reply: FastifyReply) {
    try {
      const user = await this.authService.loginUser(request.body);

      if (!user.phone) {
         // Handle cases where user might not have a phone number registered yet
         // Option: return an error, prompt user to add phone, or skip OTP
         request.log.warn(`User ${user.email} logged in but has no phone number for OTP.`);
         // For now, let's generate a standard token but they can't proceed to sensitive areas
          const tokenPayload: AuthJWTPayload = { id: user.id, email: user.email, otpVerified: false };
          const accessToken = this.fastify.jwt.sign(tokenPayload, { expiresIn: config.jwt.expiresIn });
          return reply.send({ accessToken });
         // Alternatively: throw new BadRequest("Phone number required for 2FA.");
      }

      // Credentials valid, but OTP not yet verified.
      // Issue a short-lived "pre-OTP" token.
      const otpTokenPayload: OtpJWTPayload = { id: user.id, phone: user.phone };
      const otpToken = this.fastify.jwt.sign(otpTokenPayload, { expiresIn: config.jwt.otpExpiresIn });

      // Send this short-lived token back. The client must use this
      // token to call the /auth/otp/send endpoint.
      return reply.send({ otpToken, message: "Credentials verified. Proceed to OTP verification." });

    } catch (error: any) {
       request.log.error(error, "Login failed");
       throw error; // Let error handler manage response
    }
  }

  // Handler to get current user details (requires standard JWT)
  async getMeHandler(request: FastifyRequest, reply: FastifyReply) {
    // Assumes JWT authentication middleware has run and populated request.user
    const userId = (request.user as AuthJWTPayload).id; // Type assertion using imported type
    try {
        const user = await this.authService.findUserById(userId);
        return reply.send(user);
    } catch (error) {
        request.log.error(error, `Failed to get user details for ID: ${userId}`);
        throw error;
    }
  }

  // --- OTP Handlers ---

  // This endpoint requires the short-lived 'otpToken'
  async initiateOtpHandler(request: FastifyRequest, reply: FastifyReply) {
    // Assumes JWT ('otpToken') verification middleware has run
    const otpPayload = request.user as OtpJWTPayload; // Contains id and phone, use imported type

    try {
      // NOTE: Assumes fastify.initiateSmsOtp is defined in a Sinch plugin (covered later)
      const sinchResponse = await (this.fastify as any).initiateSmsOtp(otpPayload.phone);
      // Sinch handles sending the SMS. We just need to confirm initiation.
      // The 'id' in sinchResponse is Sinch's internal verification ID,
      // we don't typically need to store or use it directly when using reportByIdentity.
      request.log.info(`OTP initiated successfully via Sinch for user ${otpPayload.id}, phone ${otpPayload.phone}`);

      // No need to send anything specific back, just confirm success.
      // The user checks their phone for the SMS.
      return reply.code(200).send({ message: `OTP sent successfully to ${otpPayload.phone.substring(0, otpPayload.phone.length - 4)}****.` });

    } catch (error: any) {
      request.log.error(error, `Failed to initiate OTP for user ${otpPayload.id}`);
      // Handle potential Sinch errors (e.g., invalid number format, rate limits)
      // The sinch plugin might throw, or we can handle specific Sinch error codes here
      if (error.response?.data?.errorCode) {
          // Example: Map Sinch error to user-friendly message
          const sinchErrorCode = error.response.data.errorCode;
           if (sinchErrorCode === 40003) { // Parameter validation failed (e.g., bad number format)
               throw new BadRequest("Invalid phone number format provided to Sinch.");
           }
           // Add more mappings as needed based on Sinch docs / testing
      }
      throw new BadRequest("Failed to send OTP. Please try again later."); // Generic fallback
    }
  }

  // This endpoint also requires the short-lived 'otpToken'
  async verifyOtpHandler(request: FastifyRequest<{ Body: VerifyOtpInput }>, reply: FastifyReply) {
     // Assumes JWT ('otpToken') verification middleware has run
     const otpPayload = request.user as OtpJWTPayload; // Contains id and phone, use imported type
     const { otp } = request.body;

     try {
         // NOTE: Assumes fastify.verifySmsOtp is defined in a Sinch plugin (covered later)
         const sinchResponse = await (this.fastify as any).verifySmsOtp(otpPayload.phone, otp);

         if (sinchResponse.status === 'SUCCESSFUL') {
             request.log.info(`OTP verification successful for user ${otpPayload.id}`);

             // OTP is correct! Issue the final, long-lived access token.
             // We need the user's email for the final payload. Fetch it.
             const user = await this.authService.findUserById(otpPayload.id);
             if (!user) throw new Unauthorized("User associated with token not found during OTP verification."); // Should not happen if token is valid

             const finalTokenPayload: AuthJWTPayload = {
                 id: user.id,
                 email: user.email,
                 otpVerified: true, // Mark as OTP verified
             };
             const accessToken = this.fastify.jwt.sign(finalTokenPayload, { expiresIn: config.jwt.expiresIn });

             // Send back the final access token
             return reply.send({ accessToken });
         } else {
             // Handle other Sinch statuses (e.g., 'FAIL', 'DENIED', 'ERROR')
             request.log.warn(`OTP verification failed for user ${otpPayload.id}. Sinch status: ${sinchResponse.status}, Reason: ${sinchResponse.reason || 'N/A'}`);
             throw new Unauthorized("Invalid or expired OTP.");
         }

     } catch (error: any) {
         request.log.error(error, `Failed to verify OTP for user ${otpPayload.id}`);
         if (error instanceof Unauthorized || error instanceof BadRequest) {
             throw error; // Re-throw known HTTP errors
         }
         // Handle potential Sinch SDK errors or other unexpected issues
         throw new BadRequest("Failed to verify OTP. Please try again later."); // Generic fallback
     }
  }
}