First, make sure you have mod_rewrite loaded:

server.modules =+ ("mod_rewrite")

Then we'll need to add this:

$HTTP["host"] == "otrs.opensu.se" {
url.rewrite = ( "^/$" => "/otrs" )
alias.url += (
"/otrs-web" => "/opt/otrs/var/httpd/htdocs",
"/otrs"     => "/opt/otrs/bin/cgi-bin",
)
$HTTP["url"] =~ "^/otrs/" {
cgi.assign = ("" => "")
index-file.names = ("index.pl")
}
debug.log-request-handling = "enable"
}