Frustrated by the Paperwork for SMS Authentication?

When building a side project or an MVP, there comes a time when you need to verify your users with real phone numbers to prevent spam and abuse. So, you look up standard SMS API providers—only to hit a massive wall of bureaucracy.

• Submitting a Business Registration Certificate
• Verifying telecom service usage
• Going through a sender ID pre-registration process

"But I'm a solo developer without a registered business yet!" Many of us have given up and compromised with simple email verification just because of these overly strict procedures.

Today, we're going to bypass all that paperwork. I'll show you how to implement a fully functional SMS verification flow in Next.js (App Router) in just 5 minutes using EasyAuth—a developer-centric SMS API that requires zero business documents.

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Solution Overview

We will use Next.js Route Handlers to keep our API keys secure on the backend, while creating a clean Client Component for the user interface. EasyAuth makes this incredibly simple by offering just two endpoints: /send and /verify.

1. Environment Setup

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

EASYAUTH_API_KEY=your_api_key_here

2. Building the Next.js Backend APIs (Route Handlers)

We need to call the EasyAuth API from our Next.js backend environment to ensure our API key isn't exposed to the client.

Send Verification Code API (app/api/auth/send/route.ts)

import { NextResponse } from 'next/server';

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

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

    if (!response.ok) throw new Error('Failed to send');
    return NextResponse.json({ success: true });
  } catch (error) {
    return NextResponse.json({ error: 'Failed to send verification code.' }, { status: 500 });
  }
}

Verify Code API (app/api/auth/verify/route.ts)

import { NextResponse } from 'next/server';

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

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

    if (!response.ok) throw new Error('Verification failed');
    return NextResponse.json({ success: true });
  } catch (error) {
    return NextResponse.json({ error: 'Invalid verification code.' }, { status: 400 });
  }
}

3. Creating the Frontend UI

Now, let's create a Client Component where users can enter their phone number and the OTP code.

'use client';

import { useState } from 'react';

export default function SmsVerification() {
  const [phone, setPhone] = useState('');
  const [code, setCode] = useState('');
  const [isSent, setIsSent] = useState(false);
  const [isVerified, setIsVerified] = useState(false);

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

  const handleVerifyCode = async () => {
    const res = await fetch('/api/auth/verify', {
      method: 'POST',
      body: JSON.stringify({ phone, code }),
    });
    
    if (res.ok) {
      setIsVerified(true);
      alert('Phone number verified successfully!');
    } else {
      alert('Incorrect verification code.');
    }
  };

  return (
    <div>
      <h2>Phone Verification</h2>
      
      <div>
         setPhone(e.target.value)}
          placeholder="Phone Number (Numbers only)"
          className="flex-1 border p-2 rounded"
          disabled={isVerified}
        /&gt;
        
          {isSent ? 'Resend' : 'Send Code'}
        
      </div>

      {isSent &amp;&amp; !isVerified &amp;&amp; (
        <div>
           setCode(e.target.value)}
            placeholder="6-digit Code"
            className="flex-1 border p-2 rounded"
          /&gt;
          
            Verify
          
        </div>
      )}
    </div>
  );
}

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Tips & Best Practices

1. Client-Side Validation Before making an API call, use regex to validate the phone number format. This prevents wasting API calls and saves you money.

2. Rate Limiting (Cooldowns) Prevent malicious users or bots from spamming the "Send Code" button. Implement a 1 to 3-minute cooldown timer after a code is sent.

3. Secure Your API Keys Never expose EASYAUTH_API_KEY to the client side. Ensure it stays strictly in your server-side Route Handlers or Server Actions (avoid using NEXT_PUBLIC_ prefixes for secrets).

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Conclusion: Why EasyAuth?

In just 5 minutes and a few lines of code, we successfully integrated a complete SMS verification flow in Next.js.

For side projects, solo developers, and startups looking to quickly test an MVP, traditional verification processes are a major roadblock. EasyAuth was built exactly to solve this developer friction.

• 🚫 Zero Paperwork: No business registration required. Solo devs can use it immediately.
• ⚡ Instant Setup: Automatic sender IDs mean no waiting for pre-registration approvals.
• 💰 Affordable Pricing: At 15-25 KRW per message, it's roughly 50% cheaper than the standard 30-50 KRW.

Sign up for EasyAuth today and get 10 free messages instantly to test your integration. Stop wasting time on bureaucratic paperwork and get back to building your core product features!