TypeScript Type Mismatch in Microsoft Authentication with Passport

import { Strategy as MicrosoftStrategy } from "passport-microsoft";

passport.serializeUser(function(user: any, done) {
  done(null, user._id);
});

passport.deserializeUser(async function(id: string, done) {

    const user = await User.findById(id).lean().exec();
    done(null, user);

});

interface IUser {
  _id: string;
  username: string;
  password?: string;
  email: string;
  firstName: string;
  lastName?: string;
  profilePicUrl?: string;
  googleId?: string;
  googleAccessToken?: string;
  googleRefreshToken?: string;
  microsoftId?: string
  microsoftAccessToken?: string
  microsoftRefreshToken?: string
  meetings: string[];
  bookings: string[];
}


declare global {
  namespace Express {
    interface Request {
      user: IUser;
    }
  }
}

router.get('/',
  passport.authenticate('microsoft', {
  }),
  function(req, res) {
    // The request will be redirected to Microsoft for authentication, so this
    // function will not be called.
  }
);

router.get('/callback',
  passport.authenticate('microsoft', { failureRedirect: '/failure' }),
  function(req, res) {
    res.redirect(`http://localhost:5173/home/event-types?firstName=${req.user.firstName}`);
  }
);

src/routes/microsoftRoutes.ts:30:70 - error TS18048: 'req.user' is possibly 'undefined'.
30     res.redirect(`http://localhost:5173/home/event-types?firstName=${req.user.firstName`);
                                                                       
src/routes/microsoftRoutes.ts:30:79 - error TS2339: Property 'firstName' does not exist on type 'User'.

30     res.redirect(`http://localhost:5173/home/event-types?firstName=${req.user.firstName`)