Frequently Asked Questions
Set up separate frontend (Next.js) and backend (Node/Express) projects. Install required dependencies like express, @vonage/server-sdk, dotenv, and cors in the backend. Create a .env file in the backend to store your Vonage API credentials and brand name securely. Initialize a Next.js project using create-next-app for the frontend.
Vonage Verify API V2 is a service for sending and verifying one-time passcodes (OTPs) via SMS and voice calls. It simplifies adding two-factor authentication (2FA) to web applications by providing a managed and reliable global service for OTP delivery and verification, reducing the complexity of building 2FA from scratch.
2FA adds a layer of security beyond passwords. By requiring users to possess their phone to receive a time-sensitive code, it significantly reduces unauthorized access even if passwords are compromised. This makes it much harder for attackers to gain access to user accounts, even if they manage to obtain the user's password through phishing or other means.
Always store the requestId server-side in a secure session for production applications. While this guide sends it to the client for demonstration simplicity, this is less secure and could be exploited. Securely storing the requestId prevents clients from manipulating it during the check process and helps prevent unauthorized use of the verification code. Use appropriate session management and secure cookie settings in a production environment.
Yes, you can request a 6-digit code by setting code_length: 6 when calling vonage.verify.start(). While the default for Verify API V1 is 4 digits, 6 is more common and provides slightly better security by increasing the number of possible combinations.
Create a POST route (e.g., /api/request-verification) in your Express backend. Extract the user's phone number from the request body, validate it, and call vonage.verify.start() with the number, brand name, and desired code length. Handle errors appropriately, and in a production setting, store the requestId in the user's server-side session.
Rate limiting is crucial to prevent abuse. Limit requests to /api/request-verification (e.g., 5 requests per 15 minutes per IP/user) to prevent SMS pumping fraud. Implement stricter limits for /api/check-verification (e.g., 5 attempts per 5 minutes) to mitigate brute-force code guessing. Use libraries like express-rate-limit for straightforward implementation.
Create a POST route (e.g., /api/check-verification) to receive the OTP code and retrieve the requestId from the user's session (secure approach). Call vonage.verify.check() with the requestId and code. A successful check returns a 200 OK status without throwing an error. Handle any errors to provide specific feedback to the user.
The Vonage Node.js SDK V3+ throws errors on API failures. Use try...catch blocks to handle them. Inspect error.response.data (for API errors) and error.response.status for specific error codes (e.g., 400, 410, 429) and provide informative error messages to the user without revealing sensitive details. Use appropriate logging for debugging and monitoring.
Never commit API keys or secrets directly into your codebase. Store them in a .env file (which should be added to your .gitignore) and load them using the dotenv library. Configure environment variables securely in your deployment environment to protect your credentials.
Use HTML input validation such as type="tel", required attribute, and input patterns to enforce basic format and improve UX. While client-side validation improves user experience by providing immediate feedback, always perform server-side validation for security.
CORS is critical when your frontend (Next.js) and backend (Express) run on different ports during development or different domains in production. Configure CORS in your backend using the cors middleware, allowing requests from the appropriate origin(s). In production, restrict CORS to your frontend's domain to enhance security.
The most secure approach is to store the requestId in a server-side session associated with the user and never send it to the client. When checking the code, retrieve the requestId from the session, preventing client-side manipulation.
A users table should contain columns for standard user information (like username, password hash). To incorporate 2FA, include columns such as is_2fa_enabled (boolean) and phone_number_for_2fa. Use database migrations to manage schema changes effectively.
Implement a 'Resend Code' button on the frontend. Upon clicking, make a request to your backend's /api/request-verification endpoint with the phone number (same logic as initial request), implementing rate limiting to prevent abuse. Update the user's session with the new requestId if storing it server-side. In the case of client-side requestId storage, send the new requestId to the client. Always enforce rate limits to prevent abuse.
Build OTP/2FA with Vonage Verify API V2, Node.js & Next.js
Learn how to implement secure SMS OTP authentication and two-factor authentication (2FA) in your Next.js application using Vonage's Verify API V2 with a Node.js/Express backend. This comprehensive tutorial covers building a production-ready OTP authentication system with phone verification, security best practices, rate limiting, error handling, and deployment strategies – everything you need to add SMS verification and two-factor authentication to protect user accounts.
Project Overview and Goals
What You'll Build:
Create a simple application demonstrating a complete SMS OTP authentication flow:
Problem Solved:
Add a critical security layer beyond traditional passwords. By requiring users to possess their phone to receive and enter a time-sensitive code, you significantly reduce the risk of unauthorized account access – even if passwords are compromised through phishing, credential stuffing, or data breaches.
Technologies Used:
@vonage/server-sdk): Simplifies interaction with the Vonage API from your Node.js backend.dotenv– Securely manage API keys and configuration variables.fetchAPI in Next.js,express.json()andcorsmiddleware in Express.System Architecture:
Prerequisites:
Expected Outcome:
By the end of this guide, you will have a functional application with SMS OTP authentication. Users can request an OTP, receive it on their phone, enter it, and have it verified. You will also understand the principles of integrating Vonage Verify V2 for phone verification, handling potential errors, and implementing security best practices.
How to Set Up Your Next.js and Node.js Project
Create separate directories for the frontend and backend for clarity.
1.1. Create Project Structure:
Open your terminal and create a main project directory, then navigate into it.
Create directories for the frontend and backend:
1.2. Backend Setup (Node.js/Express):
Navigate into the
backenddirectory:Initialize the Node.js project:
This creates a
package.jsonfile.Install necessary dependencies:
express: The web framework.@vonage/server-sdk: The official Vonage Node.js SDK (V3+ for Verify V2).dotenv: To load environment variables from a.envfile.cors: To enable Cross-Origin Resource Sharing (needed because frontend and backend run on different ports during development).Create the main server file:
Create a
.envfile to store sensitive credentials:Open the
.envfile and add your Vonage API credentials and a brand name. IMPORTANT: Replace the placeholder values (YOUR_API_KEY,YOUR_API_SECRET) with your actual credentials found on the Vonage Dashboard.Explanation of
.envVariables:VONAGE_API_KEY: Your unique identifier for accessing the Vonage API. Found on your Vonage Dashboard.VONAGE_API_SECRET: Your secret key for authenticating API requests. Found on your Vonage Dashboard. Treat this like a password.VONAGE_BRAND_NAME: The name displayed as the sender in the OTP message. Maximum 18 characters. Helps users identify the origin of the code. Must match regex pattern^[^\/{}:$]*$for security reasons.PORT: The network port your Express server will listen on.IMPORTANT: Secure Your Credentials
Create a
.gitignorefile in thebackenddirectory to prevent accidentally committing your secrets:Add the following lines to
backend/.gitignore:1.3. Frontend Setup (Next.js):
Navigate back to the root
vonage-otp-appdirectory and then into thefrontenddirectory:Create a new Next.js application using the App Router:
(Answer prompts as needed. Choose no TypeScript/Tailwind/src dir for simplicity here, but feel free to adjust).
This command scaffolds a new Next.js project in the current directory (
.).The frontend doesn't require additional dependencies for this core functionality.
Add Frontend
.gitignore:Ensure your
frontend/.gitignorefile (usually created bycreate-next-app) includes lines to ignore local environment files and build artifacts:How to Build the Vonage Verify API Backend with Node.js
Build the Express API endpoints that will interact with the Vonage Verify V2 API for SMS OTP authentication.
2.1. Basic Express Server Setup:
Open the
backend/server.jsfile and add the following initial setup:Explanation:
require('dotenv').config(): Loads variables from the.envfile intoprocess.env. Crucial for accessing credentials.new Vonage(...): Initializes the Vonage SDK client with your credentials.app.use(cors()): Allows requests from your Next.js frontend (running on a different port, e.g., 3000) to reach the backend (running on 5001). For production, configure CORS more restrictively.app.use(express.json()): Enables the server to understand incoming request bodies formatted as JSON./healthroute: A simple endpoint to check if the server is running.2.2. Implementing the
/api/request-verificationEndpoint:This endpoint receives a phone number from the frontend and triggers the Vonage OTP request using Verify V2.
Add the following route before the
app.listencall inbackend/server.js:Explanation:
/api/request-verification. It's nowasync.phoneNumberfrom the JSON request body (req.body).vonage.verify.start()(Verify V2 method) is called usingawait:number: The user's phone number (should be in E.164 format ideally, e.g., +14155552671).brand: The sender name from your.envfile.code_length: Set to 6 for a 6-digit OTP.try...catchblock handles potential errors during the API call. Vonage SDK V3+ throws errors on failure. We inspect theerrorobject (oftenerror.response.datafor API errors) to provide a more specific message and status code.requestIdHandling (Security Note): Upon success, therequest_idis returned. The code includes a prominent warning explaining that sending this to the client is less secure and refers to Section 6 for the recommended server-side session approach.2.3. Implementing the
/api/check-verificationEndpoint:This endpoint receives the
requestId(obtained from the previous step) and the OTP code entered by the user, then checks their validity with Vonage Verify V2.Add the following route before the
app.listencall inbackend/server.js:Explanation:
/api/check-verification. It'sasync.requestIdand thecodeentered by the user.vonage.verify.check()(Verify V2 method) is called usingawait:request_id: The ID of the verification attempt.code: The OTP code entered by the user.checkmethod succeeds by returning a 200 OK status without throwing an error. If theawaitcompletes without error, the code is valid.catchblock inspectserror.responseto determine the cause (e.g., status codes 400, 410, 429) and provides appropriate user feedback.How to Build the Next.js Frontend for OTP Verification
Now, let's create the user interface in Next.js to interact with our backend API for SMS OTP authentication.
3.1. Create the Page Component:
Replace the contents of
frontend/app/page.jswith the following code:Explanation:
'use client': Directive required by Next.js App Router for client-side hooks.BACKEND_URL: Points to the Express API. UsesNEXT_PUBLIC_BACKEND_URLif set.handleRequestCode: Makes the POST request to/api/request-verification. On success, stores therequestId(with the security caveat mentioned) and moves to the 'check' step.handleCheckCode: Makes the POST request to/api/check-verificationwith the storedrequestIdand the enteredcode. Shows success or error messages.verificationStep. Uses basic inline styles and provides user feedback. Inputtypeattributes are corrected to use standard quotes (e.g.,type="tel").3.2. Environment Variable for Frontend (Optional but Recommended):
Create a
.env.localfile in thefrontenddirectory to specify the backend URL during development:NEXT_PUBLIC_prefix makes this variable accessible in the browser-side code. IMPORTANT: After creating or modifying thefrontend/.env.localfile, you must restart your Next.js development server (npm run dev) for the changes to take effect.How to Test Your OTP Authentication System
Start the Backend Server: Open a terminal, navigate to the
backenddirectory, and run:You should see
Backend server listening at http://localhost:5001.Start the Frontend Server: Open another terminal, navigate to the
frontenddirectory, and run:You should see output indicating the Next.js server is running, typically at
http://localhost:3000. Remember to restart this if you just created/modified.env.local.Test the SMS OTP Flow:
http://localhost:3000in your browser.Best Practices for Error Handling and Logging
try...catchwithasync/awaitto handle errors from the Vonage SDK V3+.error.response(specificallyerror.response.statusanderror.response.data) to map Vonage API errors (like 400, 410, 429) to user-friendly messages and appropriate HTTP status codes.WinstonorPino) instead ofconsole.log/console.errorfor structured logging (JSON format), different log levels (info, warn, error), and outputting logs to files or external services.response.okand uses the JSON error message from the backend (data.error)./api/request-verificationagain (essential to implement rate limiting).async-retry), especially if network reliability is a concern.Database Schema and Secure Session Management
This simple OTP flow doesn't strictly require a database. However, in a real-world application integrating 2FA into a user system, and for more secure handling of the
requestId:userstable.is_2fa_enabled(boolean) andphone_number_for_2fato theuserstable.requestIdHandling (Recommended): The approach of sendingrequestIdto the client (used in this guide for simplicity) is less secure because the client controls it. A malicious user could potentially try to check codes against differentrequestIds. The recommended, more secure pattern uses server-side sessions:/api/request-verificationis called.requestIdin the user's server-side session (e.g., usingexpress-sessionbacked by Redis or a database store). Do NOT send therequestIdback to the client.requestId).codeto/api/check-verification.requestIdfrom the user's current session.vonage.verify.checkusing the sessionrequestIdand the submittedcode.requestIdduring the check step.knex migrationsor Prisma Migrate) if adding 2FA fields to your database schema.Essential Security Features for Production
Input Validation & Sanitization:
express-validatorto rigorously validate inputs (phoneNumberformat/length using E.164 checks,codeformat/length,requestIdformat if applicable). Sanitize inputs where necessary.required,type="tel",pattern) provides initial checks but never rely solely on frontend validation.Rate Limiting: CRITICAL for OTP endpoints.
/api/request-verification(per user ID if logged in, or per IP address) to prevent SMS pumping fraud and abuse./api/check-verification(per user ID/session, or per IP) to prevent brute-force guessing of codes.express-rate-limit(v8.1.0+ as of 2025).HTTPS: Always use HTTPS in production to encrypt data in transit. Configure your hosting environment (Vercel, Heroku, Nginx, etc.) to enforce HTTPS.
API Key Security: Never commit API keys or secrets directly into your code or version control. Use
.envfiles (added to.gitignoreas shown in setup) and configure environment variables securely in your deployment environment.CORS Configuration: In production, configure
corsrestrictively to only allow requests from your specific frontend domain(s).Secure Session Management: If implementing the recommended server-side
requestIdhandling (Section 6), use secure session middleware (express-session) with:httpOnly: true,secure: true(requires HTTPS),sameSite: 'Lax'or'Strict').Vonage Security Features: Explore Vonage Verify V2 features like fraud detection, workflow customization (e.g., SMS then Voice fallback), and Silent Authentication for enhanced security and user experience.
Frequently Asked Questions About Vonage OTP Authentication
What is Vonage Verify API V2 and how does it differ from V1?
Vonage Verify API V2 provides enhanced two-factor authentication with multiple channels (SMS, Voice, WhatsApp, Email), improved anti-fraud protection, custom webhooks, and a modernized API structure. Unlike V1, it uses a workflow-based approach and supports Silent Authentication for frictionless verification.
What Node.js version should I use for Vonage Verify API V2 in 2025?
Use Node.js v20 (Active LTS) or v22 (Active LTS) for production applications. Node.js v18 reached End-of-Life on March 27, 2025 and should no longer be used. Visit the official Node.js releases page for current LTS status.
How do I get Vonage API credentials?
Sign up for a free Vonage account at the Vonage API Dashboard. After registration, you'll find your API Key and API Secret in the "Getting Started" section of your dashboard. Store these securely in your
.envfile.What is the maximum brand name length for Vonage Verify V2?
The brand name can be up to 18 characters long and must match the regex pattern
^[^\/{}:$]*$. This is the name displayed as the sender in OTP messages, helping users identify the source of the verification code.How many digits should an OTP code be?
The Vonage Verify V2 API supports OTP codes between 4 and 10 digits. The recommended length is 6 digits, which provides a good balance between security (1 million combinations) and user convenience. Configure this with the
code_lengthparameter.What HTTP status codes does Vonage Verify V2 return?
Common status codes include: 200 (success with
{request_id, status: "completed"}), 400 (invalid code or validation error), 409 (concurrent verification not allowed), 410 (request expired or already used), and 429 (rate limit exceeded). Handle these appropriately in your error handling logic.Why shouldn't I send the requestId to the client?
Sending the
requestIdto the client allows malicious users to potentially check codes against different request IDs or manipulate the verification process. The secure approach stores therequestIdin a server-side session and only sends the verification code to the client.How do I implement rate limiting for OTP endpoints?
Use the
express-rate-limitlibrary (v8.1.0+) to limit requests per IP or user ID. Recommended limits: 5 verification requests per 15 minutes and 5 code check attempts per 5 minutes. This prevents SMS pumping fraud and brute-force attacks.What is E.164 phone number format?
E.164 is the international standard for phone numbers, starting with a + symbol followed by country code and subscriber number (e.g., +14155552671). Vonage Verify V2 requires phone numbers in E.164 format for proper routing across international carriers.
Can I use Vonage Verify V2 with TypeScript and Tailwind CSS?
Yes, this guide uses plain JavaScript and no CSS framework for simplicity, but you can easily adapt it for TypeScript (add
--typescript=yesto the Next.js setup command) and Tailwind CSS (add--tailwind=yes). The Vonage SDK supports TypeScript out of the box.How do I handle concurrent verification requests?
Vonage Verify V2 prevents concurrent verifications to the same phone number (HTTP 409 error). Inform users they must complete or cancel the current verification before requesting a new one. Implement this in your error handling with a user-friendly message.
What production security measures should I implement?
Essential security measures include: HTTPS enforcement, restrictive CORS configuration, secure session management with Redis or database-backed sessions, input validation with
express-validator, comprehensive rate limiting, proper error handling without exposing sensitive details, and storing therequestIdserver-side only.