In laravel 5.2, you can use php artisan make:auth command to generate default auth scaffold.

And you will be able to use laravel's default auth system, which using email and password as credentials.

Now, you want to use "username" instead of "email" in login page, here is how you can do it.

STEP 1: OVERRIDING FUNCTION

Lets have a look at default authentication system files,

In line number : 191 of

vendor\laravel\framework\src\Illuminate\Foundation\Auth\AuthenticatesUsers.php

There will be this function loginUsername,

   /**
     * Get the login username to be used by the controller.
     *
     * @return string
     */
    public function loginUsername()
    {
        return property_exists($this, 'username') ? $this->username : 'email';
    }

As you can see, username: 'email';

Lets override this function in app\Http\Controllers\Auth\AuthController.php

Copy and paste same function from AuthenticatesUsers.php and Paste in AuthController.php

   /**
     * Get the login username to be used by the controller.
     *
     * @return string
     */
    public function loginUsername()
    {
        return property_exists($this, 'username') ? $this->username : 'username';
    }

STEP 2: UPDATING VIEWS

Lets update resources\views\auth\login.blade.php 's login form by replacing email label, email field to textfield with a username label.

<div class="form-group{{ $errors->has('username') ? ' has-error' : '' }}">
    <label class="col-md-4 control-label">Username</label>
    <div class="col-md-6">
        <input type="text" class="form-control" name="username" value="{{ old('username') }}">
        @if ($errors->has('username'))
            <span class="help-block">
                <strong>{{ $errors->first('username') }}</strong>
            </span>
        @endif
    </div>
</div>

We are done, now you can log in with username instead of email in laravel auth scaffold.