Strange behaviour of fetch with GraphQL body

[mykhailo-alekseiev]

Hi! I'm trying to migrate my Vite project to Next.js. For authentication/authorization, I'm deciding to use the next-auth package. My app handles the session via server, so from an example, I make the auth check inside the authorize block

import { gql } from '@apollo/client';
import type { NextAuthConfig } from 'next-auth';
import { apolloClient } from './app/lib/apolloClient';
import { headers } from 'next/headers';

type AuthCheckQuery = {
  me?: {
    id: number;
    profile?: {
      first_name?: string | null;
      last_name?: string | null;
    } | null;
  } | null;
};

const AuthCheckDocument = gql`
  query AuthCheck {
    me(is_me: true) {
      id
      profile {
        first_name
        last_name
      }
    }
  }
`;

export const authConfig = {
  pages: {
    signIn: '/login',
    signOut: '/',
  },
  callbacks: {
    async authorized({ auth, request: { nextUrl } }) {
      const data: AuthCheckQuery = await fetch(process.env.API_ENDPOINT ?? '', {
        method: 'POST',
        headers: {
          'Content-Type': 'application/json',
          cookie: headers().get('cookie') ?? '',
        },
        body: JSON.stringify({
          query: AuthCheckDocument.loc?.source.body,
        }),
      }).then((res) => res.json());

      console.log('data', data);
      console.log('data?.me?.id', data?.me?.id);

      const isLoggedIn = !!data?.me?.id;
      const isOnDashboard = nextUrl.pathname.startsWith('/dashboard');
      if (isOnDashboard) {
        if (isLoggedIn) return true;
        return false; // Redirect unauthenticated users to login page
      } else if (isLoggedIn) {
        return true;
        // return Response.redirect(new URL('/dashboard', nextUrl));
      }
      return true;
    },
  },
  providers: [], // Add providers with an empty array for now
} satisfies NextAuthConfig;

As you can see, I added the console log to track the received data. And I got confused to see this logs

data {
  data: {
  me: {
  id: 163352,
  profile: { first_name: 'Name', last_name: 'Surname' }
}
}
}
data?.me?.id undefined

Could somebody explain to me where there is a bug, or I do smth wrong?