For some reason, the www/apache22 FreeBSD port does not support the mod_substitute module even though it’s bundled standard with Apache. The following patch enables building of this useful module, which compiles and works just fine out of the box.
UPDATE: After e-mailing the maintainer, this patch has been officially merged into the port as of March 29, 2011.
--- Makefile.modules.orig 2010-08-19 13:01:08.000000000 -0500
+++ Makefile.modules 2011-03-28 15:00:40.000000000 -0500
@@ -29,7 +29,7 @@
MISC_MODULES+= actions alias asis autoindex cern_meta \
cgi charset_lite dbd deflate dir dumpio env expires \
headers imagemap include info log_config logio mime \
- mime_magic negotiation rewrite setenvif speling status \
+ mime_magic negotiation rewrite setenvif speling status substitute \
unique_id userdir usertrack vhost_alias filter version reqtimeout
PROXY_MODULES= proxy proxy_connect proxy_ftp proxy_http proxy_ajp proxy_balancer proxy_scgi
SSL_MODULES= ssl
--- Makefile.options.orig 2010-08-19 13:01:08.000000000 -0500
+++ Makefile.options 2011-03-28 14:54:16.000000000 -0500
@@ -56,6 +56,7 @@
SETENVIF "Enable mod_setenvif" ON \
SPELING "Enable mod_speling" ON \
STATUS "Enable mod_status" ON \
+ SUBSTITUTE "Enable mod_substitute" OFF \
UNIQUE_ID "Enable mod_unique_id" ON \
USERDIR "Enable mod_userdir" ON \
USERTRACK "Enable mod_usertrack" ON \
--- pkg-plist.orig 2010-08-19 13:01:10.000000000 -0500
+++ pkg-plist 2011-03-28 14:57:28.000000000 -0500
@@ -79,6 +79,7 @@
include/apache22/mod_rewrite.h
include/apache22/mod_ssl.h
include/apache22/mod_status.h
+include/apache22/mod_substitute.h
include/apache22/mpm.h
include/apache22/mpm_common.h
include/apache22/mpm_default.h
@@ -164,6 +165,7 @@
%%MOD_SPELING%%libexec/apache22/mod_speling.so
%%MOD_SSL%%libexec/apache22/mod_ssl.so
%%MOD_STATUS%%libexec/apache22/mod_status.so
+%%MOD_SUBSTITUTE%%libexec/apache22/mod_substitute.so
%%MOD_SUEXEC%%libexec/apache22/mod_suexec.so
%%MOD_UNIQUE_ID%%libexec/apache22/mod_unique_id.so
%%MOD_USERDIR%%libexec/apache22/mod_userdir.so