Update Nginx config example

Closes #1103

docs/simplesamlphp-install.md

@@ -201,14 +201,11 @@ look like this:
         location ^~ /simplesaml {
             alias /var/simplesamlphp/www;
 
-            location ~ \.php(/|$) {
-                root             /var/simplesamlphp/www;
-                fastcgi_pass     127.0.0.1:9000;
-                fastcgi_index    index.php;
-                fastcgi_param    SCRIPT_FILENAME  $document_root$fastcgi_script_name;
-                fastcgi_split_path_info ^(.+?\.php)(/.*)$;
-                fastcgi_param    PATH_INFO $fastcgi_path_info;
+            location ~ ^(?<prefix>/simplesaml)(?<phpfile>.+?\.php)(?<pathinfo>/.*)?$ {
                 include          fastcgi_params;
+                fastcgi_pass     $fastcgi_pass;
+                fastcgi_param    SCRIPT_FILENAME $document_root$fastcgi_script_name;
+                fastcgi_param    SCRIPT_NAME /simplesaml$phpfile;
             }
         }
     }