How to save JWT and redirect

So at the moment I have a login setup that will return the success/failure of the login, a JWT and some user data. I'd like it to store the JWT and redirect to the page '/' when successful. When unsuccessful full it should redirect to '/users/login' and show a flash message explaining the error. Here is my current post request:

`

// Authenticate
router.post('/login', (req, res, next) => {
  const username = req.body.username;
  const password = req.body.password;

     User.getUserByEmail(username, function(err, user){
        if(err) throw err;
        if(!user){
            console.log('not user');
            // req.flash('error_msg', 'User not found');
            //
            // res.redirect('/users/login');
        return res.json({success: false, msg: 'User not found'});

        }

    User.comparePassword(password, user.password, (err, isMatch) => {
      if(err) throw err;
      if(isMatch){
        const token = jwt.sign(user, config.secret, {
          expiresIn: 604800 // 1 week
        });

        res.json({
          success: true,
          token: 'JWT '+token,
          user: {
            id: user._id,
            name: user.name,
            username: user.username,
            email: user.email
          }
        });

      } else {
       return res.json({success: false, msg: 'Wrong password'});
            // req.flash('error_msg', 'Wrong Password');
            // 
            // res.redirect('/users/login');
      }
    });
  });
});

`

The commented code will give the right result, kinda. They achieve the flash message and redirect but will do not return a value so the code will continue to run leading to errors(like trying to check the password associated with a user that doesn't exist.

I'm not sure of the best way to store a JWT, I assume cookies or something.

So what is the best way to get the desired effect, thanks, Ed.

via Ed Lynch