How to Implement Authentication in Next.js

**Issue:**
I'm looking for guidance on implementing user authentication in my Next.js application. I want to understand the best practices, libraries, and strategies for adding authentication to my project.

**Questions:**
1. What authentication libraries are commonly used with Next.js?
2. How can I protect routes that require authentication?

**Additional Information:**
- Next.js version: X.X.X
- Current authentication strategy: [insert details]

No files, tests, Next.js version, or current authentication strategy are provided. First clarify the application version and existing approach, then determine the intended authentication guidance, including library choices and route-protection practices, and document the agreed scope.

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