JWT getting renewed after accessing pages protected by middleware

[GuilhermeRPimenta]

I'm using auth.js 5.0.0-beta.25. It seems that every time the next.js middleware is called, I get a new JWT with a new expiration date. I couldn't find why does this happen.

middleware.ts:

import NextAuth from "next-auth";

import authConfig from "./lib/auth/auth.config";

const { auth } = NextAuth(authConfig);
export default auth((req) => {
  if (!req.auth) {
    return Response.redirect(new URL("/auth/login", req.url));
  }
  const pathname = req.nextUrl.pathname;
  const search = req.nextUrl.search;

  if (pathname === "/admin") {
    const url = new URL("/admin/home", req.url);
    url.search = search;
    return Response.redirect(url);
  }
});

export const config = {
  matcher: ["/admin/:path*"],
};

jwt callback:

 jwt({ token, user }) {
      if (!token.sub) {
        return token;
      }

      if (!user) return token;
      token.username = user.username;
      token.email = user.email;
      token.image = user.image;
      return token;
    },

session callback:

session({ token, session }) {
      return {
        ...session,
        token: {
          expiresAt: token.exp,
        },
        user: {
          id: token.sub,
          username: token.username as string | null,
          email: token.email as string,
          image: token.image as string | null,
        },
      };
    },