redirect /app.php to prevent duplicate content

web/.htaccess

@@ -1,10 +1,48 @@
+# Use the front controller as index file. It serves as fallback solution when
+# every other rewrite/redirect fails (e.g. in an aliased environment without
+# mod_rewrite). Additionally, this reduces the matching process for the
+# startpage (path "/") because otherwise Apache will apply the rewritting rules
+# to each configured DirectoryIndex file (e.g. index.php, index.html, index.pl).
+DirectoryIndex app.php
+
 <IfModule mod_rewrite.c>
     RewriteEngine On
 
-    #<IfModule mod_vhost_alias.c>
-    #    RewriteBase /
-    #</IfModule>
+    # Redirect to URI without front controller to prevent duplicate content
+    # (with and without `/app.php`). Only do this redirect on the initial
+    # rewrite by Apache and not on subsequent cycles. Otherwise we would get an
+    # endless redirect loop (request -> rewrite to front controller ->
+    # redirect -> request -> ...).
+    # So in case you get a "too many redirects" error or you always get redirected
+    # to the startpage because your Apache does not expose the REDIRECT_STATUS
+    # environment variable, you have 2 choices:
+    # - disable this feature by commenting the following 2 lines or
+    # - use Apache >= 2.3.9 and replace all L flags by END flags and remove the
+    #   following RewriteCond (best solution)
+    RewriteCond %{ENV:REDIRECT_STATUS} ^$
+    RewriteRule ^app\.php(/(.*)|$) %{CONTEXT_PREFIX}/$2 [R=301,L]
+
+    # If the requested filename exists, simply serve it.
+    # We only want to let Apache serve files and not directories.
+    RewriteCond %{REQUEST_FILENAME} -f
+    RewriteRule .? - [L]
+
+    # The following rewrites all other queries to the front controller. The
+    # condition ensures that if you are using Apache aliases to do mass virtual
+    # hosting, the base path will be prepended to allow proper resolution of the
+    # app.php file; it will work in non-aliased environments as well, providing
+    # a safe, one-size fits all solution.
+    RewriteCond %{REQUEST_URI}::$1 ^(/.+)(.+)::\2$
+    RewriteRule ^(.*) - [E=BASE:%1]
+    RewriteRule .? %{ENV:BASE}app.php [L]
+</IfModule>
 
-    RewriteCond %{REQUEST_FILENAME} !-f
-    RewriteRule ^(.*)$ app.php [QSA,L]
+<IfModule !mod_rewrite.c>
+    <IfModule mod_alias.c>
+        # When mod_rewrite is not available, we instruct a temporary redirect of
+        # the startpage to the front controller explicitly so that the website
+        # and the generated links can still be used.
+        RedirectMatch 302 ^/$ /app.php/
+        # RedirectTemp cannot be used instead
+    </IfModule>
 </IfModule>