Add HAProxy example

Stateless-Mode.md

@@ -71,6 +71,25 @@ Configure your webserver to respond statelessly to challenges for a given accoun
     ?>
     ```
     _NOTE that this approach uses PHP but something similar could be done with CGI, Perl, Ruby or pretty much any other server-side language._
+
+    ### HAPROXY
+
+    Add the http-request return rule to your configuration:
+    
+    ```
+    global
+        setenv ACCOUNT_THUMBPRINT '6fXAG9VyG0IahirPEU2ZerUtItW2DHzDzD9wZaEKpqd'
+        log stderr local0
+        stats socket /var/run/haproxy.sock level admin mode 0666
+
+    frontend web
+        log global
+        option httplog
+        mode  http
+        bind :80
+        bind :443 crt /etc/haproxy/certs/
+        http-request return status 200 content-type text/plain lf-string "%[path,field(-1,/)].${ACCOUNT_THUMBPRINT}\n" if { path_beg '/.well-known/acme-challenge/' }
+``` 
 3. Ok, you can issue cert now.
 
   ```