Error when installed Yii2
<p>I've install Yii2 framework using composer but get this error in my browser (on localhost):</p>
<blockquote>
<p>Invalid Configuration – yii\base\InvalidConfigException</p>
<p>yii\web\Request::cookieValidationKey must be configured with a secret key.</p>
</blockquote>
<p>How can I solve this problem?</p>