SMS Authentication: Is Paperwork Slowing Down Your Development?

If you've ever tried to add SMS authentication to a side project or startup MVP, you know the frustration. Integrating traditional SMS APIs often involves a mountain of paperwork—submitting business registration certificates, verifying telecommunication usage, and pre-registering sender IDs. You end up spending more time on admin work than writing code.

Today, we'll look at how to implement SMS authentication in a Next.js App Router environment in just 5 minutes, completely paperwork-free.

Solution Overview

• How to integrate an SMS API without document screening
• Setting up secure Route Handlers (app/api) in Next.js App Router
• A complete UI code example with client-side state management

Step 1: Building the API Routes (Server-Side)

For security reasons, third-party APIs should never be called directly from the client. We will route the requests through our Next.js backend. In this tutorial, we are using EasyAuth, a developer-friendly SMS API that requires zero paperwork to get started.

EasyAuth simplifies the process down to two intuitive endpoints: POST /send and POST /verify.

Create two files: app/api/sms/send/route.ts and app/api/sms/verify/route.ts.

import { NextResponse } from 'next/server';

// app/api/sms/send/route.ts
export async function POST(req: Request) {
  try {
    const { phone } = await req.json();

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

    const data = await response.json();
    return NextResponse.json(data);
  } catch (error) {
    return NextResponse.json({ error: 'Failed to send' }, { status: 500 });
  }
}

import { NextResponse } from 'next/server';

// app/api/sms/verify/route.ts
export async function POST(req: Request) {
  try {
    const { phone, code } = await req.json();

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

    const data = await response.json();
    return NextResponse.json(data);
  } catch (error) {
    return NextResponse.json({ error: 'Verification failed' }, { status: 500 });
  }
}

Step 2: Implementing the Client UI

Next, let's create a straightforward form in app/page.tsx where users can input their phone numbers and the OTP code. You can copy and paste this directly into your project.

'use client';
import { useState } from 'react';

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

  const handleSend = async () => {
    const res = await fetch('/api/sms/send', {
      method: 'POST',
      body: JSON.stringify({ phone })
    });
    if (res.ok) {
      alert('Verification code sent.');
      setStep(2);
    }
  };

  const handleVerify = async () => {
    const res = await fetch('/api/sms/verify', {
      method: 'POST',
      body: JSON.stringify({ phone, code })
    });
    if (res.ok) {
      alert('Verification successful!');
    } else {
      alert('Invalid verification code.');
    }
  };

  return (
    <div>
      <h2>SMS Authentication</h2>
      <div>
         setPhone(e.target.value)}
          disabled={step === 2}
          style={{ padding: '0.5rem' }}
        /&gt;
        {step === 1 ? (
          Send Code
        ) : (
          &lt;&gt;
             setCode(e.target.value)}
              style={{ padding: '0.5rem' }}
            /&gt;
            Verify
          &lt;/&gt;
        )}
      </div>
    </div>
  );
}

Tips & Best Practices

1. Environment Variables: Always store EASYAUTH_API_KEY securely in .env.local. Never expose it to the client (do not use the NEXT_PUBLIC_ prefix).
2. Rate Limiting: To prevent toll fraud or malicious SMS bombing, it is highly recommended to implement rate limiting logic at the top of your route.ts files.

Conclusion: Keep It Under 5 Minutes

By leveraging Next.js App Router's built-in Route Handlers, you can build a seamless SMS verification flow without spinning up a separate backend server.

Are you still putting off SMS integration because of the paperwork?
Meet EasyAuth, the ultimate SMS API designed for solo developers and startup MVPs.

• 📄 No Paperwork: Sign up with just an email and get your API keys instantly—no business registration required.
• ☎️ Auto Sender ID: Start sending messages right away without the hassle of pre-registering a sender number.
• 💰 Highly Affordable: Only 15~25 KRW per message, about half the cost of traditional providers.

Sign up now and get 10 free test credits to verify your integration. Stop wasting time on administrative red tape and start focusing on your core product with EasyAuth!