You have to make a router that will catch requests for a specific route and use the additional url component as a request parameter.
For example, say you have a route call rewrite and you want requests for rewrite/pink-purple to be forwarded to rewrite/index/index with a request parameter named background that would be pink-purple. Here's what the router to do this might look like Some\Module\Controller\Router.php:
<?php
namespace Some\Module\Controller;
use Magento\Framework\App\ActionFactory;
use Magento\Framework\App\ActionInterface;
use Magento\Framework\App\RequestInterface;
use Magento\Framework\App\RouterInterface;
class Router implements RouterInterface
{
protected $actionFactory;
public function __construct(ActionFactory $actionFactory)
{
$this->actionFactory = $actionFactory;
}
/**
* @param RequestInterface $request
* @return ActionInterface
*/
public function match(RequestInterface $request)
{
$path = trim($request->getPathInfo(), '/');
$parts = explode('/', $path);
if ($parts && $parts[0] === 'rewrite') {
if (isset($parts[1])) {
$request->setParams(['background' => $parts[1]]);
}
$request->setModuleName('rewrite')
->setControllerName('index')
->setActionName('index');
/** @var ActionInterface */
return $this->actionFactory->create('Magento\Framework\App\Action\Forward');
}
return null;
}
}
Now you have to add the router to the router list. In etc/frontend/di.xml you have this:
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
<type name="Magento\Framework\App\RouterList">
<arguments>
<argument name="routerList" xsi:type="array">
<item name="paramsRedirect" xsi:type="array">
<item name="class" xsi:type="string">Some\Module\Controller\Router</item>
<item name="disable" xsi:type="boolean">false</item>
<item name="sortOrder" xsi:type="string">50</item>
</item>
</argument>
</arguments>
</type>
</config>
