Update configuring-well-known.md

docs/configuring-well-known.md

@@ -110,6 +110,25 @@ server {
 proxy /.well-known/matrix https://matrix.DOMAIN
 ```
 
+**For HAProxy**, it would be something like this:
+
+```haproxy
+frontend www-https
+	# Select a Challenge for Matrix federation redirect
+	acl matrix-acl path_beg /.well-known/matrix/
+	# Use the challenge backend if the challenge is set
+	use_backend matrix-backend if matrix-acl
+backend matrix-backend
+	# Redirects the .well-known matrix to the matrix server for federation.
+	http-request set-header Host matrix.example.com
+	server matrix matrix.example.com:80
+	# Map url path as ProxyPass does
+	reqirep ^(GET|POST|HEAD)\ /.well-known/matrix/(.*) \1\ /\2
+	# Rewrite redirects as ProxyPassReverse does
+	acl response-is-redirect res.hdr(Location) -m found
+	rsprep ^Location:\ (http|https)://matrix.example.com\/(.*) Location:\ \1://matrix.exapmle.com/.well-known/matrix/\2 if response-is-redirect
+```
+
 Make sure to:
 
 - **replace `DOMAIN`** in the server configuration with your actual domain name