Fixing ‘Next-Auth TypeError [ERR_INVALID_URL]’ in Next.js Projects

Understanding the ‘Invalid URL’ Error in Next.js

When working with Next.js and employing Next-Auth for authentication, encountering a ‘Next-Auth TypeError [ERR_INVALID_URL]’ can be a sign of an issue with how the URLs are configured. This error usually appears when Next-Auth cannot parse the environment variables pertaining to URLs due to their improper format. Specifically, this might involve incorrect values for NEXTAUTH_URL or a database connection URL.

Common Causes and Solutions

The error generally stems from one of the following scenarios: an incorrectly set environmental variable, the omission of necessary environmental variables, or a syntax error in the URL string. Addressing these issues involves checking and updating your project’s .env.local file where your environment variables are stored.

First, ensure that the NEXTAUTH_URL environment variable is correctly set. This variable tells Next-Auth where your application is running and should match the canonical URL of your site. For a local development server, this will usually be ‘http://localhost:3000’ or the port you’re running your development server on.

Secondly, if you’re using a database with Next-Auth, verify that your database URL is valid. Database connection strings sometimes include special characters that need to be URL encoded. If they’re not, Next-Auth might throw an ‘Invalid URL’ error when trying to connect.

Lastly, the syntax of the NEXTAUTH_URL or your database URL might have typographical errors. Ensure that you don’t have any trailing slashes, spaces, or missing parts of the URL such as the protocol (http:// or https://).

Configure NEXTAUTH_URL for Different Environments

For your application to function correctly across various environments (local development, staging, production), you should configure the NEXTAUTH_URL for each respective environment. You can manage this by defining your environment variables within .env.local for local development, and using environment-specific variables in your deployment solution for staging and production.

Here’s how you can set up NEXTAUTH_URL in your .env.local file for local development:

NEXTAUTH_URL=http://localhost:3000

And for a production environment, you might set it in your deployment environment settings:

NEXTAUTH_URL=https://your-production-domain.com

Working Example

We’ll now walk through a simple Next.js app setup using Next-Auth where these environment variables are configured correctly. Here’s an example of how you might structure your application:

// .env.local
NEXTAUTH_URL=http://localhost:3000
DATABASE_URL='your-database-connection-url'

// pages/api/auth/[...nextauth].js
import NextAuth from 'next-auth'
import Providers from 'next-auth/providers'

export default NextAuth({
  providers: [
    Providers.GitHub({
      clientId: process.env.GITHUB_ID,
      clientSecret: process.env.GITHUB_SECRET
    })
    // Add other providers as needed
  ],
  database: process.env.DATABASE_URL
})

// Deploying to production
// Make sure you setup production environment variables correctly on your hosting provider.

Ensure your .env.local file and production environment variables are set with the correct formatting, without typos or syntax errors. Now your Next.js app with Next-Auth should connect without issues, and you won’t encounter the ‘Invalid URL’ error.

In cases where you’re confident that your URLs are correct, yet you’re still facing the error, this could be due to an updated or misconfigured dependency or an aspect of Next.js not behaving as expected. In such scenarios, checking the Next.js and Next-Auth release notes for updates or breaking changes and ensuring you’re using compatible versions might resolve the issue.