nixos/nextcloud: add documentation for alternative reverse-proxies

Follow-up for #93584[1]. This change adds a simple example how to use
`Nextcloud` with `httpd`.

[1] https://github.com/NixOS/nixpkgs/pull/93584#discussion_r465233063

nixos/modules/services/web-apps/nextcloud.nix

@@ -47,8 +47,18 @@ let
 in {
 
   imports = [
-    ( mkRemovedOptionModule [ "services" "nextcloud" "nginx" "enable" ]
-      "The nextcloud module dropped support for other webservers than nginx.")
+    (mkRemovedOptionModule [ "services" "nextcloud" "nginx" "enable" ] ''
+      The nextcloud module supports `nginx` as reverse-proxy by default and doesn't
+      support other reverse-proxies officially.
+
+      However it's possible to use an alternative reverse-proxy by
+
+        * disabling nginx
+        * setting `listen.owner` & `listen.group` in the phpfpm-pool to a different value
+
+      Further details about this can be found in the `Nextcloud`-section of the NixOS-manual
+      (which can be openend e.g. by running `nixos-help`).
+    '')
   ];
 
   options.services.nextcloud = {

nixos/modules/services/web-apps/nextcloud.xml

@@ -123,6 +123,61 @@
   </para>
  </section>
 
+ <section xml:id="module-services-nextcloud-httpd">
+  <title>Using an alternative webserver as reverse-proxy (e.g. <literal>httpd</literal>)</title>
+  <para>
+   By default, <package>nginx</package> is used as reverse-proxy for <package>nextcloud</package>.
+   However, it's possible to use e.g. <package>httpd</package> by explicitly disabling
+   <package>nginx</package> using <xref linkend="opt-services.nginx.enable" /> and fixing the
+   settings <literal>listen.owner</literal> &amp; <literal>listen.group</literal> in the
+   <link linkend="opt-services.phpfpm.pools">corresponding <literal>phpfpm</literal> pool</link>.
+  </para>
+  <para>
+   An exemplary configuration may look like this:
+<programlisting>{ config, lib, pkgs, ... }: {
+  <link linkend="opt-services.nginx.enable">services.nginx.enable</link> = false;
+  services.nextcloud = {
+    <link linkend="opt-services.nextcloud.enable">enable</link> = true;
+    <link linkend="opt-services.nextcloud.hostName">hostName</link> = "localhost";
+
+    /* further, required options */
+  };
+  <link linkend="opt-services.phpfpm.pools._name_.settings">services.phpfpm.pools.nextcloud.settings</link> = {
+    "listen.owner" = config.services.httpd.user;
+    "listen.group" = config.services.httpd.group;
+  };
+  services.httpd = {
+    <link linkend="opt-services.httpd.enable">enable</link> = true;
+    <link linkend="opt-services.httpd.adminAddr">adminAddr</link> = "webmaster@localhost";
+    <link linkend="opt-services.httpd.extraModules">extraModules</link> = [ "proxy_fcgi" ];
+    virtualHosts."localhost" = {
+      <link linkend="opt-services.httpd.virtualHosts._name_.documentRoot">documentRoot</link> = config.services.nextcloud.package;
+      <link linkend="opt-services.httpd.virtualHosts._name_.extraConfig">extraConfig</link> = ''
+        &lt;Directory "${config.services.nextcloud.package}"&gt;
+          &lt;FilesMatch "\.php$"&gt;
+            &lt;If "-f %{REQUEST_FILENAME}"&gt;
+              SetHandler "proxy:unix:${config.services.phpfpm.pools.nextcloud.socket}|fcgi://localhost/"
+            &lt;/If&gt;
+          &lt;/FilesMatch&gt;
+          &lt;IfModule mod_rewrite.c&gt;
+            RewriteEngine On
+            RewriteBase /
+            RewriteRule ^index\.php$ - [L]
+            RewriteCond %{REQUEST_FILENAME} !-f
+            RewriteCond %{REQUEST_FILENAME} !-d
+            RewriteRule . /index.php [L]
+          &lt;/IfModule&gt;
+          DirectoryIndex index.php
+          Require all granted
+          Options +FollowSymLinks
+        &lt;/Directory&gt;
+      '';
+    };
+  };
+}</programlisting>
+  </para>
+ </section>
+
  <section xml:id="module-services-nextcloud-maintainer-info">
   <title>Maintainer information</title>