Add support for Jitsi discovery for Riot via /.well-known/matrix/client

This will not work yet, as no version of Riot currently supports it.
It's expected to land in riot-web v1.5.16 via matrix-org/matrix-react-sdk#4348.

group_vars/matrix_servers

@@ -18,6 +18,8 @@
 
 matrix_identity_server_url: "{{ 'https://' + matrix_synapse_trusted_third_party_id_servers[0] if matrix_synapse_trusted_third_party_id_servers|length > 0 else None }}"
 
+matrix_riot_jitsi_preferredDomain: "{{ matrix_server_fqn_jitsi if matrix_jitsi_enabled else '' }}"
+
 ######################################################################
 #
 # /matrix-base

roles/matrix-base/defaults/main.yml

@@ -43,6 +43,11 @@ matrix_identity_server_url: ~
 matrix_integration_manager_rest_url: ~
 matrix_integration_manager_ui_url: ~
 
+# The domain name where a Jitsi server is self-hosted.
+# If set, `/.well-known/matrix/client` will suggest Riot clients to use that Jitsi server.
+# See: https://github.com/vector-im/riot-web/blob/develop/docs/jitsi.md#configuring-riot-to-use-your-self-hosted-jitsi-server
+matrix_riot_jitsi_preferredDomain: ''
+
 # The Docker network that all services would be put into
 matrix_docker_network: "matrix"
 

roles/matrix-base/templates/static-files/well-known/matrix-client.j2

@@ -18,4 +18,9 @@
 		]
 	}
 	{% endif %}
+	{% if matrix_riot_jitsi_preferredDomain %},
+	"im.vector.riot.jitsi": {
+		"preferredDomain": {{ matrix_riot_jitsi_preferredDomain|to_json }}
+	}
+	{% endif %}
 }