getSession() and unstable_getServerSession() always return null

[iHarryD]

I have an internal api route endpoint in my app at which I'm trying to get the session using unstable_getServerSession, but I'm always getting null returned from it. Could someone tell me why is this happening, and how to make it work.

[jozefhruska]

Could you send some code snippets or, ideally, a reproducible example?

[iHarryD]

import Cors from "cors"; 
  
 const cors = Cors({ 
   methods: ["GET", "POST", "DELETE"], 
   credentials: true, 
   origin: "http://localhost:3000", 
 }); 
  
 function runMiddleware( 
   req: NextApiRequest, 
   res: NextApiResponse, 
   func: (req: NextApiRequest, res: NextApiResponse, callback: any) => any 
 ) { 
   return new Promise((resolve, reject) => { 
     func(req, res, (result: any) => { 
       if (result instanceof Error) { 
         return reject(result); 
       } 
       return resolve(result); 
     }); 
   }); 
 } 
  
 export default async function (req: NextApiRequest, res: NextApiResponse) { 
   await runMiddleware(req, res, cors); 
   const { method } = req; 
   const connection: { clientPromise: null | MongoClient } = { 
     clientPromise: null, 
   }; 
   try { 
     switch (method) { 
       case "POST": 
         const validation = postValidation(req.body); 
         if (validation.error) 
           return res 
             .status(500) 
             .json({ message: validation.error.details[0].message }); 
  
         const session = await unstable_getServerSession( 
           req, 
           res, 
           nextAuthConfig 
         ); 
         if (session === null) 
           return res.status(300).json({ message: "Unauthorized" });

Basically this is my code on the server.
From the front-end, I'm just sending a fetch request with POST method and body containing data.