文档确实没有写，但是我们可以看看源码

Auth方法的实现都在 Illuminate\Auth\Guard里面

    /**
     * Attempt to authenticate a user using the given credentials.
     *
     * @param  array  $credentials
     * @param  bool   $remember
     * @param  bool   $login
     * @return bool
     */
    public function attempt(array $credentials = [], $remember = false, $login = true)
    {
        $this->fireAttemptEvent($credentials, $remember, $login);

        $this->lastAttempted = $user = $this->provider->retrieveByCredentials($credentials);            
        
        // 看这里
        // If an implementation of UserInterface was returned, we'll ask the provider
        // to validate the user against the given credentials, and if they are in
        // fact valid we'll log the users into the application and return true.
        if ($this->hasValidCredentials($user, $credentials)) {
            if ($login) {
                $this->login($user, $remember);
            }

            return true;
        }

        return false;
    }
    
    /**
     * Determine if the user matches the credentials.
     *
     * @param  mixed  $user
     * @param  array  $credentials
     * @return bool
     */
    protected function hasValidCredentials($user, $credentials)
    {
        // 执行认证驱动器的validCredentials方法
        return ! is_null($user) && $this->provider->validateCredentials($user, $credentials);
    }

默认是使用eloquent作为认证驱动器，所以看看Illuminate\Auth\EloquentUserProvider里面的实现

    public function validateCredentials(UserContract $user, array $credentials)
    {
        $plain = $credentials['password'];

        return $this->hasher->check($plain, $user->getAuthPassword());
    }

所以如果要改验证的逻辑，可以继承原有的驱动器，然后重写validateCredentials里面的逻辑

class TestUserProvider extend EloquentUserProvider
{
    public function validateCredentials(UserContract $user, array $credentials)
    {
        $plain = $credentials['password'];

        return md5($plain) == $user->getAuthPassword();
    }
}

最后设置驱动器，建议加载AppServiceProvider的boot()里面

Auth::setProvider(new TestUserProvider());

文档里有写！不要偷懒不看文档，你最近提的问题都是文档里写的。