Added versioning to API endpoints, allowing not to pass the version which will default to v1

module/Rest/src/Middleware/PathVersionMiddleware.php

@@ -0,0 +1,54 @@
+<?php
+namespace Shlinkio\Shlink\Rest\Middleware;
+
+use Psr\Http\Message\ResponseInterface as Response;
+use Psr\Http\Message\ServerRequestInterface as Request;
+use Zend\Stratigility\MiddlewareInterface;
+
+class PathVersionMiddleware implements MiddlewareInterface
+{
+    /**
+     * Process an incoming request and/or response.
+     *
+     * Accepts a server-side request and a response instance, and does
+     * something with them.
+     *
+     * If the response is not complete and/or further processing would not
+     * interfere with the work done in the middleware, or if the middleware
+     * wants to delegate to another process, it can use the `$out` callable
+     * if present.
+     *
+     * If the middleware does not return a value, execution of the current
+     * request is considered complete, and the response instance provided will
+     * be considered the response to return.
+     *
+     * Alternately, the middleware may return a response instance.
+     *
+     * Often, middleware will `return $out();`, with the assumption that a
+     * later middleware will return a response.
+     *
+     * @param Request $request
+     * @param Response $response
+     * @param null|callable $out
+     * @return null|Response
+     */
+    public function __invoke(Request $request, Response $response, callable $out = null)
+    {
+        $uri = $request->getUri();
+        $path = $uri->getPath();
+
+        // If the path does not begin with the version number, prepend v1 by default for retrocompatibility purposes
+        if (strpos($path, '/rest/v') !== 0) {
+            $parts = explode('/', $path);
+            // Remove the first empty part and the "/rest" prefix
+            array_shift($parts);
+            array_shift($parts);
+            // Prepend the prefix with version
+            array_unshift($parts, '/rest/v1');
+
+            $request = $request->withUri($uri->withPath(implode('/', $parts)));
+        }
+
+        return $out($request, $response);
+    }
+}