Created a config prost-processor which adds the base path on every applicable configuration

config/autoload/router.global.php

@@ -6,6 +6,8 @@ use Zend\Expressive\Router\FastRouteRouter;
 return [
 
     'router' => [
+        'base_path' => '',
+
         'fastroute' => [
             FastRouteRouter::CONFIG_CACHE_ENABLED => true,
             FastRouteRouter::CONFIG_CACHE_FILE => 'data/cache/fastroute_cached_routes.php',

config/config.php

@@ -28,5 +28,6 @@ return (new ConfigAggregator\ConfigAggregator([
         ? new ConfigAggregator\PhpFileProvider('config/test/*.global.php')
         : new ConfigAggregator\ZendConfigProvider('config/params/{generated_config.php,*.config.{php,json}}'),
 ], 'data/cache/app_config.php', [
-    Core\SimplifiedConfigParser::class,
+    Core\Config\SimplifiedConfigParser::class,
+    Core\Config\BasePathPrefixer::class,
 ]))->getMergedConfig();

module/Core/src/Config/BasePathPrefixer.php

@@ -0,0 +1,39 @@
+<?php
+declare(strict_types=1);
+
+namespace Shlinkio\Shlink\Core\Config;
+
+use function Functional\map;
+
+class BasePathPrefixer
+{
+    public function __invoke(array $config): array
+    {
+        $basePath = $config['router']['base_path'] ?? '';
+        $config['routes'] = $this->prefixRoutesWithBasePath($config, $basePath);
+        $config['middleware_pipeline'] = $this->prefixMiddlewarePathsWithBasePath($config, $basePath);
+        $config['url_shortener']['domain']['hostname'] .= $basePath;
+
+        return $config;
+    }
+
+    private function prefixRoutesWithBasePath(array $config, string $basePath): array
+    {
+        return map($config['routes'] ?? [], function (array $route) use ($basePath) {
+            $route['path'] = $basePath . $route['path'];
+            return $route;
+        });
+    }
+
+    private function prefixMiddlewarePathsWithBasePath(array $config, string $basePath): array
+    {
+        return map($config['middleware_pipeline'] ?? [], function (array $middleware) use ($basePath) {
+            if (! isset($middleware['path'])) {
+                return $middleware;
+            }
+
+            $middleware['path'] = $basePath . $middleware['path'];
+            return $middleware;
+        });
+    }
+}

module/Core/src/Config/SimplifiedConfigParser.php

@@ -1,7 +1,7 @@
 <?php
 declare(strict_types=1);
 
-namespace Shlinkio\Shlink\Core;
+namespace Shlinkio\Shlink\Core\Config;
 
 use Shlinkio\Shlink\Installer\Util\PathCollection;
 use Zend\Stdlib\ArrayUtils;
@@ -22,6 +22,7 @@ class SimplifiedConfigParser
         'db_config' => ['entity_manager', 'connection'],
         'delete_short_url_threshold' => ['delete_short_urls', 'visits_threshold'],
         'redis_servers' => ['redis', 'servers'],
+        'base_path' => ['router', 'base_path'],
     ];
     private const SIMPLIFIED_CONFIG_SIDE_EFFECTS = [
         'not_found_redirect_to' => [

module/Core/test/Config/SimplifiedConfigParserTest.php

@@ -1,10 +1,10 @@
 <?php
 declare(strict_types=1);
 
-namespace ShlinkioTest\Shlink\Core;
+namespace ShlinkioTest\Shlink\Core\Config;
 
 use PHPUnit\Framework\TestCase;
-use Shlinkio\Shlink\Core\SimplifiedConfigParser;
+use Shlinkio\Shlink\Core\Config\SimplifiedConfigParser;
 
 use function array_merge;
 
@@ -50,6 +50,7 @@ class SimplifiedConfigParserTest extends TestCase
                 'password' => 'bar',
                 'port' => '1234',
             ],
+            'base_path' => '/foo/bar',
         ];
         $expected = [
             'app_options' => [
@@ -96,6 +97,10 @@ class SimplifiedConfigParserTest extends TestCase
                     'tcp://1.2.2.2:2222',
                 ],
             ],
+
+            'router' => [
+                'base_path' => '/foo/bar',
+            ],
         ];
 
         $result = ($this->postProcessor)(array_merge($config, $simplified));