services: httpd: Allow using it with PHP.

* gnu/services/web.scm (httpd): Make existing httpd-module API public.
* doc/guix.texi (Apache HTTP Server): Document its usage with PHP-FPM.

Signed-off-by: Christopher Baines <mail@cbaines.net>

doc/guix.texi

@@ -50,6 +50,7 @@ Copyright @copyright{} 2018 Oleg Pykhalov@*
 Copyright @copyright{} 2018 Mike Gerwitz@*
 Copyright @copyright{} 2018 Pierre-Antoine Rouby@*
 Copyright @copyright{} 2018 Gábor Boskovits@*
+Copyright @copyright{} 2018 Florian Pelz@*
 
 Permission is granted to copy, distribute and/or modify this document
 under the terms of the GNU Free Documentation License, Version 1.3 or
@@ -16612,6 +16613,10 @@ within the store, for example @code{(file-append mod-wsgi
 @end table
 @end deffn
 
+@defvr {Scheme Variable} %default-httpd-modules
+A default list of @code{httpd-module} objects.
+@end defvr
+
 @deffn {Data Type} httpd-config-file
 This data type represents a configuration file for the httpd service.
 
@@ -16620,6 +16625,32 @@ This data type represents a configuration file for the httpd service.
 The modules to load. Additional modules can be added here, or loaded by
 additional configuration.
 
+For example, in order to handle requests for PHP files, you can use Apache’s
+@code{mod_proxy_fcgi} module along with @code{php-fpm-service-type}:
+
+@example
+(service httpd-service-type
+         (httpd-configuration
+          (config
+           (httpd-config-file
+            (modules (cons*
+                      (httpd-module
+                       (name "proxy_module")
+                       (file "modules/mod_proxy.so"))
+                      (httpd-module
+                       (name "proxy_fcgi_module")
+                       (file "modules/mod_proxy_fcgi.so"))
+                      %default-httpd-modules))
+            (extra-config (list "\
+<FilesMatch \\.php$>
+    SetHandler \"proxy:unix:/var/run/php-fpm.sock|fcgi://localhost/\"
+</FilesMatch>"))))))
+(service php-fpm-service-type
+         (php-fpm-configuration
+          (socket "/var/run/php-fpm.sock")
+          (socket-group "httpd")))
+@end example
+
 @item @code{server-root} (default: @code{httpd})
 The @code{ServerRoot} in the configuration file, defaults to the httpd
 package. Directives including @code{Include} and @code{LoadModule} are

gnu/services/web.scm

@@ -70,6 +70,11 @@
             httpd-config-file-user
             httpd-config-file-group
 
+            <httpd-module>
+            httpd-module
+            httpd-module?
+            %default-httpd-modules
+
             httpd-service-type
 
             <nginx-configuration>