Next.js app router with tRPC context and NextAuth

// route.ts
import { fetchRequestHandler } from '@trpc/server/adapters/fetch';
import { createContext } from '@/server/context';
import { appRouter } from '@/server/routers/app';

const handler = (req: Request) =>
  fetchRequestHandler({
    endpoint: '/api/trpc',
    req,
    router: appRouter,
    createContext,
    batching: {
      enabled: true,
    },
  });

export { handler as GET, handler as POST };

// context.ts
import * as trpc from '@trpc/server';
import * as trpcNext from '@trpc/server/adapters/fetch';
import { NodeHTTPCreateContextFnOptions } from '@trpc/server/adapters/node-http';
import { IncomingMessage } from 'node:http';
import ws from 'ws';
import { getSession } from 'next-auth/react';

export async function createContext(
  opts:
    | NodeHTTPCreateContextFnOptions<IncomingMessage, ws>
    | trpcNext.FetchCreateContextFnOptions
) {
  const req = opts?.req;

  const session = req && (await getSession({ req }));

  return {
    req,
    session,
  };
}

export type Context = trpc.inferAsyncReturnType<typeof createContext>;