How to do Login authentication with many to many relationship table field.

Add use hash to LoginController:

use Illuminate\Support\Facades\Hash;

Overwrite login method in your LoginController:

public function login(Request $request)
    {
        $this->validate([
        'email' => 'required|string',
        'password' => 'required|string',
                'group_id' => 'nullable|integer',    
        ]);

       
        if ($this->hasTooManyLoginAttempts($request)) {
            $this->fireLockoutEvent($request);

            return $this->sendLockoutResponse($request);
        }
    if ($request->group_id) {
        $group = Group::find($request->group_id);
        $user = $group->users()->where('email', $request->email)->first();
                if ($user && Hash::check($request->password, $hashedPassword)) {
            return $this->sendLoginResponse($request);  
        }
    } else if ($this->attemptLogin($request)) {
        return $this->sendLoginResponse($request);  
        }
        $this->incrementLoginAttempts($request);

        return $this->sendFailedLoginResponse($request);
    }