Have You Given Up on Adding SMS Verification to Your Side Project?

When building a web application or an app, SMS verification (OTP) is highly recommended for preventing spam bots and verifying user identities. However, implementing it often introduces a massive roadblock. Traditional SMS gateway providers demand a mountain of paperwork: Business Registration Certificates, strict sender ID pre-registration, and proofs of telecommunication usage.

"How is a solo developer building a weekend toy project, or a startup testing an MVP, supposed to handle all this bureaucracy?"

If you've asked yourself this question, you're in the right place. In this tutorial, we will explore how to perfectly implement phone verification in a Next.js App Router environment in just 5 minutes using EasyAuth—without submitting a single document.

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Next.js App Router SMS Authentication Guide

The App Router, introduced in Next.js 13, allows developers to safely build backend APIs within their frontend projects using Route Handlers. This pattern ensures that your API keys are never exposed to the client.

1. Setting up Environment Variables

First, add your EasyAuth API key to the .env.local file at the root of your project.

EASYAUTH_API_KEY=your_api_key_here

2. OTP Send API (app/api/auth/send/route.ts)

This route will receive the phone number from the client and forward it to EasyAuth's /send endpoint.

import { NextResponse } from 'next/server';

export async function POST(request: Request) {
  try {
    const { phone } = await request.json();

    // Sending OTP via EasyAuth API
    const response = await fetch('https://api.easyauth.io/send', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${process.env.EASYAUTH_API_KEY}`
      },
      body: JSON.stringify({ to: phone })
    });

    if (!response.ok) throw new Error('Failed to send SMS');

    return NextResponse.json({ success: true, message: 'Verification code sent.' });
  } catch (error) {
    return NextResponse.json({ success: false, error: 'Server error occurred.' }, { status: 500 });
  }
}

3. OTP Verification API (app/api/auth/verify/route.ts)

Next, create a Route Handler to verify the OTP code entered by the user.

import { NextResponse } from 'next/server';

export async function POST(request: Request) {
  try {
    const { phone, code } = await request.json();

    // Verifying OTP via EasyAuth API
    const response = await fetch('https://api.easyauth.io/verify', {
      method: 'POST',
      headers: {
        'Content-Type': 'application/json',
        'Authorization': `Bearer ${process.env.EASYAUTH_API_KEY}`
      },
      body: JSON.stringify({ phone, code })
    });

    const data = await response.json();

    if (!data.isValid) {
      return NextResponse.json({ success: false, message: 'Invalid verification code.' }, { status: 400 });
    }

    return NextResponse.json({ success: true, message: 'Verification successful.' });
  } catch (error) {
    return NextResponse.json({ success: false, error: 'Server error occurred.' }, { status: 500 });
  }
}

4. Implementing the Client UI (app/page.tsx)

Now, let's build the Client Component where users will interact to input their phone number and the OTP code.

'use client';

import { useState } from 'react';

export default function PhoneVerification() {
  const [phone, setPhone] = useState('');
  const [code, setCode] = useState('');
  const [step, setStep] = useState(1);
  const [loading, setLoading] = useState(false);

  const handleSendCode = async () => {
    setLoading(true);
    const res = await fetch('/api/auth/send', {
      method: 'POST',
      body: JSON.stringify({ phone }),
    });
    if (res.ok) setStep(2);
    else alert('Failed to send code.');
    setLoading(false);
  };

  const handleVerifyCode = async () => {
    setLoading(true);
    const res = await fetch('/api/auth/verify', {
      method: 'POST',
      body: JSON.stringify({ phone, code }),
    });
    const data = await res.json();
    if (data.success) {
      alert('Verification successful!');
      // Proceed to next signup step
    } else {
      alert(data.message);
    }
    setLoading(false);
  };

  return (
    <div>
      <h2>Phone Verification</h2>
      
      <div>
         setPhone(e.target.value)}
          disabled={step === 2}
          className="w-full p-2 border rounded"
        /&gt;
      </div>

      {step === 1 ? (
        
          {loading ? 'Sending...' : 'Get Verification Code'}
        
      ) : (
        <div>
           setCode(e.target.value)}
            className="w-full p-2 border rounded"
          /&gt;
          
            {loading ? 'Verifying...' : 'Verify'}
          
        </div>
      )}
    </div>
  );
}

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Security Tips & Best Practices

1. Rate Limiting: To prevent malicious users from spamming SMS APIs and draining your funds, implement rate limiting by IP address. Integrating tools like Upstash Redis makes this incredibly straightforward.
2. Input Validation: Use libraries like Zod to rigorously validate the phone number format on the server side before calling the API, ensuring you don't waste API calls on invalid numbers.

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Conclusion: EasyAuth, The Developer-Friendly SMS API

We successfully implemented a seamless SMS authentication flow combining Next.js App Router and a simple API, without dealing with any bureaucratic nightmares.

If you need to integrate phone verification into your side project, freelance work, or startup MVP today, try EasyAuth—the simplest SMS authentication API built for developers.

• 📄 Zero Paperwork: Absolutely no need to submit business registrations or telecommunication proofs.
• 🚀 Immediate Start: Set up and integrate the API within 5 minutes of signing up. (Automatic sender number provided).
• 💰 Reasonable Pricing: While traditional services charge 30-50 KRW per SMS, EasyAuth only costs 15-25 KRW.
• 🎁 Free Trial: Get 10 free SMS credits immediately upon registration to test your integration.

Skip the tedious paperwork and focus purely on what matters: building your awesome product!