4 KiB
ACME
Synapse v1.0 requires that federation TLS certificates are verifiable by a trusted root CA. If you do not already have a valid certificate for your domain, the easiest way to get one is with Synapse's new ACME support, which will use the ACME protocol to provision a certificate automatically. By default, certificates will be obtained from the publicly trusted CA Let's Encrypt.
For a sample configuration, please inspect the new ACME section in the example
generated config by running the generate-config executable. For example::
~/synapse/env3/bin/generate-config
You will need to provide Let's Encrypt (or another ACME provider) access to
your Synapse ACME challenge responder on port 80, at the domain of your
homeserver. This requires you to either change the port of the ACME listener
provided by Synapse to a high port and reverse proxy to it, or use a tool
like authbind to allow Synapse to listen on port 80 without root access.
(Do not run Synapse with root permissions!) Detailed instructions are
available under "ACME setup" below.
If you are already using self-signed certificates, you will need to back up
or delete them (files example.com.tls.crt and example.com.tls.key in
Synapse's root directory), Synapse's ACME implementation will not overwrite
them.
You may wish to use alternate methods such as Certbot to obtain a certificate from Let's Encrypt, depending on your server configuration. Of course, if you already have a valid certificate for your homeserver's domain, that can be placed in Synapse's config directory without the need for any ACME setup.
ACME setup
Synapse v1.0 will require valid TLS certificates for communication between servers
(port 8448 by default) in addition to those that are client-facing (port
443). In the case that your server_name config variable is the same as
the hostname that the client connects to, then the same certificate can be
used between client and federation ports without issue. Synapse v0.99.0+
will provision server-to-server certificates automatically for you for
free through Let's Encrypt if you tell it to.
In order for Synapse to complete the ACME challenge to provision a certificate, it needs access to port 80. Typically listening on port 80 is only granted to applications running as root. There are thus two solutions to this problem.
Using a reverse proxy
A reverse proxy such as Apache or nginx allows a single process (the web server) to listen on port 80 and proxy traffic to the appropriate program running on your server. It is the recommended method for setting up ACME as it allows you to use your existing webserver while also allowing Synapse to provision certificates as needed.
For nginx users, add the following line to your existing server block:
location /.well-known/acme-challenge {
proxy_pass http://localhost:8009/;
}
For Apache, add the following to your existing webserver config::
ProxyPass /.well-known/acme-challenge http://localhost:8009/.well-known/acme-challenge
Make sure to restart/reload your webserver after making changes.
Authbind
authbind allows a program which does not run as root to bind to
low-numbered ports in a controlled way. The setup is simpler, but requires a
webserver not to already be running on port 80. This includes every time
Synapse renews a certificate, which may be cumbersome if you usually run a
web server on port 80. Nevertheless, if you're sure port 80 is not being used
for any other purpose then all that is necessary is the following:
Install authbind. For example, on Debian/Ubuntu:
sudo apt-get install authbind
Allow authbind to bind port 80:
sudo touch /etc/authbind/byport/80
sudo chmod 777 /etc/authbind/byport/80
When Synapse is started, use the following syntax::
authbind --deep <synapse start command>
Finally, once Synapse is able to listen on port 80 for ACME challenge
requests, it must be told to perform ACME provisioning by setting enabled
to true under the acme section in homeserver.yaml:
acme:
enabled: true