Support for Multi-Domain NextAuth Configuration in Single App Service Deployment (Azure AD)

[iris-debiprasad]

Hi NextAuth team 👋,

We’re encountering a problem while using NextAuth.js with Azure AD provider in a multi-domain setup on a single Next.js app service deployment.

Context

• Framework: Next.js

• Auth Provider: Microsoft Azure AD

• Auth Library: NextAuth.js

• Deployment: Single App Service (e.g., Azure App Service)

• Domains:

• https://nowoptic.dev1.com
  

• https://nowoptic.dev2.com
  

Both domains point to the same deployed Next.js app. We use NextAuth.js for authentication with Azure AD, which requires setting the NEXTAUTH_URL environment variable to generate the proper redirect URI (i.e., https:///api/auth/callback/azure-ad).

The Problem
Since there is only one environment per app service, we can only set a single NEXTAUTH_URL, which causes issues when:

• Users from both domains attempt to log in at the same time.
• The app dynamically attempts to infer the correct domain inside middleware.ts or _app.tsx (e.g., using request.headers.host) and override NEXTAUTH_URL, but this breaks in concurrent sessions.
• Race conditions or incorrect redirects occur because modifying global process.env at runtime is not safe in server environments.

What We Tried

• Dynamically rewriting the NEXTAUTH_URL in middleware or _app.tsx depending on the domain:
  Works partially but is not safe for concurrent users.
  Leads to interference between user sessions from different domains.
• Setting up domain-specific redirect URIs in Azure AD — but Azure AD expects static registered redirect URLs.

What We’re Looking For

1. Is there any supported or recommended way to make NextAuth.js work in multi-domain scenarios, where each domain needs its own NEXTAUTH_URL, but the app codebase and deployment is shared?
2. Can NEXTAUTH_URL be inferred/request-scoped instead of being a static global value?
3. Any guidance or patterns others have successfully used in similar Azure AD + Next.js multi-tenant/multi-domain scenarios?