Guide: HAProxy HTTP Basic Authentication for specific sites (SSL Termination)

Objective

I use HAProxy to serve multiple SSL/TLS enabled sites with HAProxy doing SSL termination. The sites serve regular HTTP while users see proper HTTPS sites (with free certificates from LetsEncrypt). My objective was to provide HTTP Basic Authentication as a second layer of protection for certain applications like NextCloud (DropBox clone) or Gitea (GitHub clone).

Challenges

I wanted to provide HTTP Basic Auth over specific services (not all which is much easier) which didn’t natively support them like Gitea. Secondly, I wanted it to be transparent to the underlying Application. Thirdly, I didn’t want to provide plain-text passwords in haproxy.cfg.

Solution

After few iterations I arrived at a simple solution to the problem. The steps are:

1. Create users with encrypted passwords
   
2. Add users to haproxy.cfg
3. Force authentication for specific sites on frontend
4. Remove authorization on backend

Create users with encrypted passwords

To create encrypted passwords, you need a tool called mkpasswd which is available with whois, so you need to install it first (one time activity):

sudo apt install whois

Create password as shown below (replace Password with your actual Password):

mkpasswd -m sha-512 Password

Copy the encrypted password generated by the tool (mkpasswd).

Add users to haproxy.cfg

You can add multiple user lists as well as user groups (beyond the scope of this guide) to haproxy. Let’s create an user list named AuthUsers (as an example):

userlist AuthUsers
        user Username1 password $6$d./LYD0vplX$XoPWiTQfhNt4g4NRcU/toFiV89xhW524abcdfg
        user Username2 password $6$d./LYD0vplX$XoPWiTQfhNt4g4NRcU/toFefghxhW524abcdfg

Replace Username1, Username2 with your actual user names and the corresponding encrypted password as the last argument in the line.

You can add as many users as you want.

Force authentication for specific sites only

Let’s say we want to force authentication for these two sites (in frontend section):

acl host_example1 hdr(host) -i example1.com
acl host_example1 hdr(host) -i example2.com

Below this we force them to be authenticated:

acl authorized http_auth(AuthUsers)
http-request auth realm Example1 if host_example1 !authorized
http-request auth realm Example2 if host_example2 !authorized

Use backend only when properly authenticated:

use_backend example1 if host_example1 authorized
use_backend example2 if host_cexample2 authorized

Remove authentication header from backend

HAProxy for some strange reason sends this Authorization header to backend which sends certain servers in a loop. it is advisable to remove it.

backend example1
http-request set-header X-Client-IP %[src]
server example1 example1:3000 check
http-request del-header Authorization

backend example2
http-request set-header X-Client-IP %[src]
server example2 example2:3000 check
http-request del-header Authorization

Now restart the haproxy server and voila!