Introduction

In april 2020 Conversations released a new version with support for end-to-end encrypted audio/video calls, bringing that functionality to one of the most widely used XMPP clients. For A/V calls to work you need to enable server-side support. This guide will help you doing that.

We will first install and configure Coturn. It is a libre STUN/TURN server that helps establish peer connections across firewalls for media streams such as calls. Then we will configure Prosody so that it can give temporary credentials to an XMPP clients to login to Coturn.

Like the other guides, this one assumes Debian stable running on the server, the fact that you will end up hosting a few of your friends and that you have some basic skills working on a linux command line.

Furthermore it assumes you have already installed and configured Prosody. If you haven’t, take a look at our guide ‘Configuring an XMPP server for secure, mobile instant messaging’ first.

Set up firewall

To make your server communicate make sure following ports are open in your firewall for UDP traffic:

3478 (TURN)
5349 (TURN + TLS)
49152-65535 (UDP endpoints for clients)

Set up Coturn

First install Coturn

$ sudo apt-get update && sudo apt-get install coturn

After installing first make a backup of the existing configuration:

$ sudo mv /etc/turnserver.conf /etc/turnserver.conf.bak

Then download the configuration by the homebrewserver.club:

$ cd ~
$ wget https://homebrewserver.club/downloads/turnserver.conf -O turnserver.conf

The file looks like this:

## Minimal version of /etc/turnserver.conf 
## For more options and info see the original /etc/turnserver.conf.bak

# Which porst to listen on, make sure the corresponding ports are accepting UDP connections on your firewall
listening-port=3478
tls-listening-port=5349

# Your machine's IP addres
# This is either the external IP or, in the case you are behind a NAT, the IP of the machine in the NAT
listening-ip=CUSTOMIZE THIS

# Your domain name
realm=myserver.org

# Ports that client can connect to. Again make sure they are open for UDP connections on your firewall
min-port=49152
max-port=65535

# For the connection with Prosody. Generate a long passphrase for the secret.
use-auth-secret
static-auth-secret=CUSTOMIZE THIS

#Paths to Let's Encrypt certificates
cert=/etc/letsencrypt/live/myserver.org/cert.pem
pkey=/etc/letsencrypt/live/myserver.org/privkey.pem

# Log to syslog
syslog

# For security:
# disallow server fingerprinting
prod
#dissalow connections on lo interface
no-loopback-peers
# disable command-line access 
no-cli

Now time for some config. You need to edit /etc/tunserver.conf in a few places.

First, add your servers’ IP-address to listening-ip.

In case you are behind a NAT, for example when you are hosting from home and are making use of port forwarding this will be a local IP adress. If your machine is directly exposed to the internet, that is the external IP-addres.

If you don’t know it, you can find out using the following command:

$ ip --oneline addr show primary | grep -E '(en|eth)'

After that make sure realm points to the domain name of the server.

Then, set static-auth-secret to a decently long passphrase. You can also generate one with:

$ openssl rand -base64 30

Take note of it because we will need this secret later.

Finally, edit the paths to the Let’s Encrypt certificates to whatever you’ve set in ‘Configuring an XMPP server for secure, mobile instant messaging’.

Once you are done move it in to place:

$ sudo mv turnserver.conf /etc/turnserver.conf

Then uncomment TURNSERVER_ENABLED=1 in /etc/default/coturn.

Update & set up Prosody

First update your Prosody modules:

$ apt-get install mercurial
$ cd /usr/src/prosody-modules
$ hg pull
$ hg update

Then edit your prosody config in /etc/prosody/prosody.cfg.lua:

First add turncredentials to the modules_enabled section.

Then, before the ‘Virtual Hosts’ section, add:

turncredentials_host = "myserver.org"
turncredentials_secret="mydecentlylongpassphrase"

And replace the value of turncredentials_secret with the value of static-auth-secret in /etc/turnserver.conf and turncredentials_host with your domain name.

Finishing up

Start coturn and enable it start on boot

$ sudo systemctl enable --now coturn

Restart prosody

$ /etc/init.d/prosody restart

Finally to see if it works, you can check your server with the web-based Conversations Compliance tester you should look out for the status of ‘XEP-0215’ in the ‘Results for informational tests’ section.

Troubleshooting

In case you run in to issues have a look at the notes by Daniel Gultsch for how to debug issues. Furthermore you can try either the Conversations.im or Homebrewserver.club channels.

Thanks & Acknowledgements

Based on example config by Wiktor Kwapisiewicz, and the Prosody documentation