Why AUTH_URL Is Required in Production for Next Auth (Auth.js v5)

Overview

When deploying an application using Next Auth (Auth.js v5) to a Docker container or production environment, the following error occurs with GitHub OAuth authentication if the AUTH_URL environment variable is not configured:

Development Environment vs Production Environment

Development Environment (npm run dev)

In the development environment, Next.js automatically detects host information, so configuring AUTH_URL is not required.

Production Environment (Docker / npm run build && npm start)

In the production environment, Next Auth cannot automatically detect host information, so configuring AUTH_URL is required.

Docker Configuration Examples

Using docker run

Using docker-compose.yml

List of Required Environment Variables

.env.local Example

Why This Problem Occurs

1. Development environment: The Next.js development server can obtain accurate host information from request headers
2. Production environment: Inside a Docker container, it starts as 0.0.0.0:3000, so it does not know the actual URL when accessed from outside
3. OAuth mechanism: GitHub only allows redirects to URLs that exactly match the registered redirect_uri

Troubleshooting

Error: “redirect_uri is not associated with this application”

Cause: AUTH_URL is not configured, or it does not match the GitHub OAuth App’s Callback URL

Solution:

1. Configure AUTH_URL correctly
2. Set {AUTH_URL}/api/auth/callback/github as the “Authorization callback URL” in the GitHub OAuth App

Error: “UntrustedHost: Host must be trusted”

Cause: AUTH_TRUST_HOST is not configured

Solution: Add AUTH_TRUST_HOST=true to the environment variables

Reference Links

• Auth.js Documentation
• Auth.js Environment Variables
• GitHub OAuth Apps

Created: 2026-01-27