[Azure AD B2C] OperationProcessingError: response is not a conform Authorization Server Metadata response in v5.0.0-beta.28

Environment

System:

• OS: Windows 11 Pro

Binaries:

• Node: 20.17.0
• npm: 10.8.2
• pnpm: 10.12.4

Browsers:

• Chrome: 138.0.7204.158

npm packages:

• "@auth/core": "^0.40.0",
• "next": "15.4.3",
• "next-auth": "^5.0.0-beta.28",
• "react": "19.1.0",
• "react-dom": "19.1.0"

Reproduction URL

https://github.com/DharmiVekariya/NextjsAzureADB2C

Describe the issue

Hi team,

I have implemented Azure AD B2C authentication flow using next-auth@4.24.11 as per the official documentation, and everything is working perfectly — I get the expected tokens and session.

However, after upgrading to next-auth@5.0.0-beta.28, I encountered the following error at runtime:

ERROR
[auth][error] OperationProcessingError: "response" is not a conform Authorization Server Metadata response (unexpected HTTP status code)

Unfortunately, the error message is unclear, and I'm not sure what the actual cause is. It breaks during authentication. All environment variables are set correctly.

Please let me know if I’m missing any required changes for v5 beta compatibility with Azure AD B2C.

How to reproduce

To reproduce

• Add Azure Configuration in .env.local file
• Run application with npm run dev
• Open http://localhost:3000/ in a browser
• Click on SignIn button and it will show the error in terminal

Expected behavior

The expected behavior is that the user should be redirected to the Microsoft login screen, and after a successful login, redirected back to the application.

Start with the linked reproduction repository, its Azure configuration in .env.local, and the listed next-auth, @auth/core, Next.js, and React versions. Run npm run dev, reproduce the sign-in failure, and compare the metadata response with the expected redirect to Microsoft login and successful callback.