メールアドレス以外のカラムで認証を行う

/**
    * Get the login username to be used by the controller.
    *
    * @return string
    */
public function username()
{
    return '<認証に使用するカラム名>';
}

<?php

namespace App\Http\Controllers\Auth;

use App\Http\Controllers\Controller;
use App\Providers\RouteServiceProvider;
use Illuminate\Foundation\Auth\AuthenticatesUsers;

class LoginController extends Controller
{
    /*
    |--------------------------------------------------------------------------
    | Login Controller
    |--------------------------------------------------------------------------
    |
    | This controller handles authenticating users for the application and
    | redirecting them to your home screen. The controller uses a trait
    | to conveniently provide its functionality to your applications.
    |
    */

    use AuthenticatesUsers;

    /**
     * Where to redirect users after login.
     *
     * @var string
     */
    protected $redirectTo = RouteServiceProvider::HOME;

    /**
     * Create a new controller instance.
     *
     * @return void
     */
    public function __construct()
    {
        $this->middleware('guest')->except('logout');
    }
}

/**
 * Handle a login request to the application.
 *
 * @param  \Illuminate\Http\Request  $request
 * @return \Illuminate\Http\RedirectResponse|\Illuminate\Http\Response|\Illuminate\Http\JsonResponse
 *
 * @throws \Illuminate\Validation\ValidationException
 */
public function login(Request $request)
{
    $this->validateLogin($request);

    // If the class is using the ThrottlesLogins trait, we can automatically throttle
    // the login attempts for this application. We'll key this by the username and
    // the IP address of the client making these requests into this application.
    if (method_exists($this, 'hasTooManyLoginAttempts') &&
        $this->hasTooManyLoginAttempts($request)) {
        $this->fireLockoutEvent($request);

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

    if ($this->attemptLogin($request)) {
        if ($request->hasSession()) {
            $request->session()->put('auth.password_confirmed_at', time());
        }

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

    // If the login attempt was unsuccessful we will increment the number of attempts
    // to login and redirect the user back to the login form. Of course, when this
    // user surpasses their maximum number of attempts they will get locked out.
    $this->incrementLoginAttempts($request);

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

/**
 * Validate the user login request.
 *
 * @param  \Illuminate\Http\Request  $request
 * @return void
 *
 * @throws \Illuminate\Validation\ValidationException
 */
protected function validateLogin(Request $request)
{
    $request->validate([
        $this->username() => 'required|string',
        'password' => 'required|string',
    ]);
}

/**
 * Get the login username to be used by the controller.
 *
 * @return string
 */
public function username()
{
    return 'email';
}