Developer Guide: Building Inbound Two-Way SMS with Next.js, NextAuth, and Sinch - code-examples -

Frequently Asked Questions

This guide provides a step-by-step process to integrate Sinch's inbound SMS capabilities into your Next.js application. It utilizes NextAuth.js for user authentication and Prisma for database interactions, allowing you to securely receive and process SMS messages sent to a dedicated Sinch number linked to user accounts.
NextAuth.js simplifies the implementation of user authentication in your Next.js application. This is crucial for associating incoming SMS messages with specific authenticated user accounts based on their registered phone numbers.
E.164 format (+15551234567) ensures consistent handling of phone numbers, which is essential for reliably linking inbound SMS messages from Sinch to the corresponding user account. It is a globally recognized standard that enables phone number validation, verification and compatibility across different systems, preventing errors or mismatches caused by regional variations.
The Sinch SDK is optional for this specific guide, which focuses on receiving inbound SMS messages. However, the SDK is required if you extend the functionality to send replies or other outbound communications.
While this guide uses PostgreSQL, you can adapt it to use other databases by adjusting the `DATABASE_URL` and configuring the appropriate Prisma provider in the `schema.prisma` file.
Webhook security is paramount. Generate a strong secret with `openssl rand -base64 32` and configure it in both your `.env` file (`SINCH_WEBHOOK_SECRET`) and the Sinch dashboard for the specific webhook endpoint. This secret will be used to verify the signature of incoming webhook requests, ensuring they originate from Sinch and not malicious actors.
The diagram visually illustrates the flow of requests and data between the user, your Next.js application, the Sinch platform, and the database. It highlights the interactions with NextAuth.js for login requests and Prisma for database access, and showcases how the webhooks are processed via an API route.
Use tools like ngrok or the Vercel CLI to expose your local development server to the internet. This will allow Sinch to send webhooks to your local endpoint during development and testing. Make sure to configure the generated URL from ngrok or Vercel as your webhook URL in Sinch.
You'll need Node.js, access to a PostgreSQL database, a Sinch account with API credentials and a dedicated phone number, and basic understanding of React, TypeScript, and REST APIs.
The application assumes that SMS messages are sent in E.164 format. It looks up the user in the database whose `phoneNumber` field matches the incoming `fromNumber` received in the Sinch webhook payload. Accurate and consistent use of E.164 is critical for correct user identification.
The guide is designed for Next.js version 14 or later, using the App Router.
Prisma is a modern Object-Relational Mapper (ORM) that simplifies database interactions. It provides a type-safe way to access and manipulate data in your PostgreSQL database, including creating, updating, and querying users and message data.
TypeScript adds static typing to your project, which improves code maintainability, developer experience with enhanced autocompletion and error detection, and helps catch errors early in development. It's recommended to leverage TypeScript in any large-scale Next.js application.
User passwords are securely hashed using bcryptjs before being stored in the database. This ensures that even if the database is compromised, the raw passwords remain protected.
This guide doesn't explicitly cover deployment steps, however common platforms for deploying a Next.js app include Vercel, Netlify, AWS Amplify, or Google Cloud Run. In your chosen production environment, ensure your environment variables are correctly set, and database connections configured.