Frequently Asked Questions
Integrate the Vonage Verify API into your Node.js/Express app to implement two-factor authentication. This involves setting up API endpoints to request an OTP, which is sent to the user's phone via SMS, and then verifying the OTP submitted by the user. The Vonage API handles code generation, delivery, and verification.
The Vonage Verify API simplifies the implementation of two-factor authentication (2FA) by generating, delivering (via SMS and potentially voice), and verifying one-time passwords (OTPs). It streamlines the process and reduces development time compared to building an OTP system from scratch.
Vonage Verify API handles secure code generation, multi-channel delivery, retries, code expiry, and verification, reducing development time and potential security risks. It simplifies a complex process into easy API calls, offering a more robust solution than building it yourself.
While Express 4.16+ has built-in body parsing middleware, explicitly using body-parser can improve clarity or ensure compatibility, especially in projects using older Express versions or when more explicit parsing configuration is needed.
Yes, you can customize the sender name (brand) that appears in the SMS message sent by the Vonage Verify API. When calling vonage.verify.start(), set the brand parameter to your application's name. This clearly identifies the source of the OTP to the user.
Make a POST request to the /request-otp endpoint of your Node.js application, providing the user's phone number in E.164 format (e.g., +14155552671) in the request body. The server will then interact with the Vonage Verify API to initiate the OTP process.
Send a POST request to your server's /check-otp endpoint including both the phone number and the received OTP code. The backend will compare this code against the Vonage Verify API using the associated request ID. Never expose the request_id directly to the client for security best practices.
The Vonage API Key and Secret are your credentials to access the Vonage APIs, including the Verify API. Find them on your Vonage API Dashboard. Store them securely, typically in a .env file, never directly in your code.
The Vonage Verify API returns a status code in its responses. '0' indicates success. Non-zero statuses represent specific errors. Check the result.status and result.error_text to identify the cause of the failure and handle appropriately.
The user sends their phone number; the Node.js app requests an OTP from Vonage; Vonage sends an SMS to the user; the user submits the code; the app verifies the code with Vonage and sends back success/failure.
Using a database or cache ensures data isn't lost if the server restarts, making the system scalable. It also allows secure linking between verification requests and individual user sessions.
Add columns to your Users table to store the Vonage request_id and an optional expiry timestamp. Alternatively, use a separate table linked to user_id to store pending verification details.
If the initial SMS fails, Vonage will fallback to a text-to-speech (TTS) phone call that reads out the code. You can also configure custom workflows for different fallback strategies.
Framework Note: This guide demonstrates OTP/2FA implementation using Node.js with Express.js. While the title references Next.js and Supabase, this implementation focuses on Express.js backend patterns that adapt to Next.js API routes and integrate with Supabase Auth for user management. Express.js provides simplicity and widespread adoption in backend API development, making the core concepts transferable across frameworks.
This guide provides a step-by-step walkthrough for building a production-ready One-Time Password (OTP) Two-Factor Authentication (2FA) system using SMS delivery. You'll leverage Node.js with the Express framework and the Vonage Verify API for a robust and simplified implementation.
By the end of this tutorial, you'll have a functional application that:
This guide focuses on the core backend logic and API endpoints necessary for SMS OTP verification.
Project Overview and Goals
Goal: Implement a secure and reliable SMS-based 2FA mechanism for user verification within a Node.js/Express application.
Problem Solved: Standard password authentication remains vulnerable to multiple attack vectors including credential stuffing (automated injection of stolen username/password pairs), phishing attacks, brute-force attacks, and password reuse exploits (source: OWASP Multifactor Authentication Cheat Sheet). Microsoft research indicates that MFA would have prevented 99.9% of account compromises (source). Adding 2FA via SMS OTP significantly enhances security by requiring users to possess their registered phone ("something they have") in addition to their password ("something they know"). This guide provides the backend infrastructure for this second factor.
Security Limitations: While SMS-based 2FA is significantly better than password-only authentication, it remains susceptible to SIM swapping attacks, SMS interception, and phishing. For high-security applications, consider TOTP authenticator apps or hardware tokens (source: OWASP MFA Testing Guide).
Technologies Used:
@vonage/server-sdk: The official Vonage Node.js SDK for interacting with Vonage APIs, including the Verify API (npm package).dotenv: A module to load environment variables from a.envfile intoprocess.env.body-parser: Node.js middleware for parsing incoming request bodies. While newer versions of Express (4.16+) have built-in middleware (express.json(),express.urlencoded()), includingbody-parserexplicitly ensures compatibility or can make parsing setup clearer for some developers.Compatibility Note: The
@vonage/server-sdkrequires Node.js 18 LTS or higher. Express.js 4.x is compatible with all LTS Node.js versions.Why Vonage Verify API?
Instead of manually generating codes, managing delivery attempts, handling expiry, and implementing complex verification logic, the Vonage Verify API encapsulates this entire workflow. It provides:
This significantly reduces development time and potential security pitfalls compared to building an OTP system from scratch.
System Architecture:
Diagram Description:
startendpoint with the user's number.request_idto the Node.js application.request_idand calls the Vonage Verify API'scheckendpoint with therequest_idand the submitted code.Security Note: All communication between the client and server must use HTTPS/TLS to prevent man-in-the-middle (MITM) attacks that could intercept OTP codes or session tokens. Communication between your server and Vonage API is automatically secured via HTTPS.
Prerequisites:
curlor Postman: For testing the API endpoints.1. Setting Up the Project
Create the basic project structure and install the necessary dependencies.
1.1 Create Project Directory:
Open your terminal or command prompt and create a new directory for your project.
1.2 Initialize Node.js Project:
Initialize the project using npm. The
-yflag accepts the default settings.This creates a
package.jsonfile.1.3 Install Dependencies:
Install Express, the Vonage Server SDK,
dotenvfor environment variables, andbody-parser.Optional but Recommended for Production:
express: The web framework.@vonage/server-sdk: To interact with the Vonage APIs (latest version recommended).dotenv: To manage sensitive credentials like API keys.body-parser: Middleware to parse JSON request bodies.express-rate-limit: Middleware for rate limiting to prevent abuse (npm package).libphonenumber-js: Library for phone number validation and formatting (npm package).1.4 Create Project Structure:
Create the following basic file structure:
1.5 Configure
.gitignore:Create a
.gitignorefile in the root directory and add the following lines to prevent committing sensitive information and unnecessary files:1.6 Set Up Environment Variables (
.env):Create a file named
.envin the root directory. Find your API Key and API Secret on the Vonage API Dashboard.Replace
YOUR_API_KEY_HEREandYOUR_API_SECRET_HEREwith your actual credentials from the Vonage dashboard.Vonage Free Tier: New Vonage accounts receive €2 free credit. Each verification attempt costs approximately €0.05-0.15 depending on destination country, allowing 13-40 test verifications. Check current pricing at Vonage Pricing.
Purpose: Using environment variables is crucial for security. It prevents hardcoding sensitive credentials directly into your source code.
dotenvloads these variables intoprocess.envwhen the application starts.2. Implementing Core Functionality (Vonage Verify API)
Now, write the core logic in
index.jsto interact with the Vonage Verify API.2.1 Initialize Express and Vonage SDK:
Open
index.jsand add the following setup code:Explanation:
require('dotenv').config();: Loads variables from the.envfile. Call this early in your application.express,body-parser, and theVonageclass from the SDK, plus rate limiting and phone validation libraries.expressapp and sets theport.Vonageclient using the API key and secret loaded fromprocess.env. Includes a check to ensure the keys are present./request-otp, and 10 verification attempts per 5 minutes per IP for/check-otp(OWASP recommendation).bodyParsermiddleware to correctly parse incoming JSON and URL-encoded request bodies.verificationRequests: A simple JavaScript object used as temporary storage to map phone numbers to therequest_idreturned by Vonage. Note: This is for demonstration only. In production, use Redis or a database.validateAndFormatPhone()helper function usinglibphonenumber-jsto validate and convert phone numbers to E.164 format, which Vonage requires./healthendpoint for monitoring and load balancer health checks.2.2 Implement OTP Request Route (
/request-otp):Add the following route handler in
index.jswithin the// --- Routes ---section:Key Improvements:
libphonenumber-jsto validate and format numbers to E.164 before sending to Vonage API.request_idto the client.workflow_id: 6(SMS only) to avoid unexpected voice calls. Default workflow (1) includes voice fallback after 125 seconds (source).Vonage Verify Status Codes Reference:
Source: Vonage Verify API Status Codes
2.3 Implement OTP Check Route (
/check-otp):Add the route handler for verifying the code submitted by the user:
Key Improvements:
Vonage Verify Check Status Codes:
Source: Vonage Verify API Status Codes
3. Building a Complete API Layer
You've now defined the core API endpoints with security enhancements:
GET /health: Health check endpoint for monitoring.POST /request-otp: Initiates the verification process (rate limited: 5 per 15 min per IP).POST /check-otp: Verifies the submitted code (rate limited: 10 per 5 min per IP).Vonage Verify Workflow Configuration:
The Vonage Verify API supports 7 predefined workflows for delivering OTP codes (source):
Recommendation: Use
workflow_id: 6(SMS-only) to avoid unexpected voice calls and associated costs. The default workflow (1) will attempt voice calls after 125 seconds if the code isn't verified.Security Considerations – HTTPS Requirement:
All production deployments must use HTTPS to prevent:
Use services like Let's Encrypt for free SSL/TLS certificates, or deploy behind a reverse proxy (nginx, Cloudflare) that handles TLS termination.
API Documentation & Testing Examples:
Here are examples using
curlto test the endpoints. Replace placeholders accordingly.3.1 Test Health Check:
Expected Response:
3.2 Test Requesting an OTP:
(Replace
+14155552671with a real phone number you can receive SMS on, in E.164 format.)Expected Success Response (200 OK):
(You should receive an SMS on the target phone within seconds.)
Example Error Response (400 Bad Request – Invalid format):
3.3 Test Checking an OTP:
(Use the same phone number as above and the code received via SMS.)
Expected Success Response (200 OK):
Example Error Response (401 Unauthorized – Wrong Code):
Example Error Response (429 Too Many Requests):
4. Security Considerations
Critical Security Requirements:
HTTPS Only: All production deployments must use HTTPS. Never transmit OTP codes or credentials over HTTP.
Rate Limiting: Implemented via
express-rate-limit:/request-otp: Max 5 requests per 15 minutes per IP/check-otp: Max 10 attempts per 5 minutes per IPInput Validation & Sanitization:
libphonenumber-jsbefore API callsAttempt Limiting:
Session Management: (Production requirement)
request_idwith authenticated user session, not just phone numberhttpOnly,secure, andsameSiteflagsexpress-session:Data Privacy & GDPR Compliance:
+1415555****Prevent Replay Attacks:
request_idcan only be verified once (Vonage enforces)Secret Management:
.envfiles to version controlOWASP Recommendations for MFA:
5. Database Schema and Data Layer (Production)
For production, replace the in-memory
verificationRequestsobject with a persistent store.Option 1: Redis (Recommended for OTP storage)
Redis provides fast key-value storage with built-in expiration, ideal for temporary verification data.
Option 2: PostgreSQL Database Schema
For applications with existing user databases:
Integration Example with Database:
6. Troubleshooting and Common Issues
Issue: SMS Not Received
Possible causes:
Issue: "Throttled" Error (Status 1)
Cause: Exceeding 30 requests/second to Vonage API (source).
Solution: Implement request queuing or reduce request rate.
Issue: "Invalid credentials" (Status 4)
Causes:
VONAGE_API_KEYorVONAGE_API_SECRETin.envdotenv.config()is called first)Solution: Verify credentials on Vonage Dashboard.
Issue: Code Expired (Status 16)
Default expiration: 300 seconds (5 minutes) for workflow 6.
Solution: Request a new code. Consider increasing
pin_expiryparameter up to 3600s (1 hour).Issue: Rate Limit Errors (429)
Cause: Application-level rate limiting triggered (5 requests per 15 min).
Solution: Wait for the cooldown period or adjust rate limit configuration for your use case.
International SMS Delivery Challenges:
Consult Vonage country-specific guides for requirements.
Debugging Tips:
Enable detailed logging:
Test with a known working number first.
Check Vonage API logs on the dashboard for detailed error messages.
Verify environment variables are loaded:
7. Next Steps and Production Deployment
Production Readiness Checklist:
Docker Deployment Example:
Docker Compose with Redis:
Advanced Features to Consider:
Additional Resources:
Conclusion:
This guide provides a comprehensive implementation of SMS-based OTP 2FA using Node.js, Express, and the Vonage Verify API. The implementation includes essential security features like rate limiting, input validation, and proper error handling. For production use, migrate from in-memory storage to Redis or a database, implement proper user session management, deploy over HTTPS, and consider the advanced security features discussed.
While SMS 2FA is a significant security improvement over password-only authentication, consider offering users the option to upgrade to TOTP-based authenticators or hardware security keys for enhanced protection against SIM-swap and phishing attacks.