fixed the middleware bypass risk

[chauhan-varun]

PR Fixes:

• Middleware Authentication Bypass

Resolves #1831

Fix Implementation

1. Middleware Layer (/src/middleware.ts):

   • Block and reject x-middleware-subrequest header manipulation
   • Remove client-provided g headers
   • Add timestamp validation

2. API Validation (/src/lib/validateAuthHeader.ts):

   • Created reusable validation helper
   • Implemented defense-in-depth validation

Verification

The security fix was verified using curl to attempt the exploit:

curl -i -H "x-middleware-subrequest: src/middleware:src/middleware:src/middleware" -H "g: {\"id\":1,\"email\":\"[email protected]\"}" "http://localhost:3000/api/mobile/search?q=web"

Result: HTTP/1.1 403 Forbidden with {"message":"Unauthorized"} response

Checklist before requesting a review
I have performed a self-review of my code
I assure there is no similar/duplicate pull request regarding same issue