title: Yii2 URL rule - passing parameter based on pattern
body: <p>I have a controller/action: <code>site/signup</code> That takes parameter <code>campaign</code></p>
  
  <p>My rule is: </p>
  
  <pre><code>[
      'pattern' =&gt; '&lt;controller&gt;/&lt;action&gt;',
      'route' =&gt; '&lt;controller&gt;/&lt;action&gt;',
      'suffix' =&gt; '.html'
  ]
  </code></pre>
  
  <p>My action definition is:</p>
  
  <pre><code>public function actionSignup($package = 'trial', $campaign = null, $invite = null){}
  </code></pre>
  
  <p>What I want to achieve is to create URL alias as such:</p>
  
  <pre><code>http://something.com/twitter
  </code></pre>
  
  <p>That would open <code>site/signup</code> with <code>$campaign = 'twitter'</code></p>
  
  <p>I thought this rule would work:</p>
  
  <pre><code>'twitter' =&gt; 'site/signup&lt;campaign:twitter&gt;'
  </code></pre>
  
  <p>But unfortunately it doesnt. Is there any easy way to achieve this?</p>
  
  <p>Thank you</p>