Add Sygnal support

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/683

docs/configuring-playbook-sygnal.md

@@ -0,0 +1,71 @@
+# Setting up Sygnal (optional)
+
+The playbook can install and configure the [Sygnal](https://github.com/matrix-org/sygnal) push gateway for you.
+
+See the project's [documentation](https://github.com/matrix-org/sygnal) to learn what it does and why it might be useful to you.
+
+**Note**: most people don't need to install their own gateway. As Sygnal's [Notes for application developers](https://github.com/matrix-org/sygnal/blob/master/docs/applications.md) documentation says:
+
+> It is not feasible to allow end-users to configure their own Sygnal instance, because the Sygnal instance needs the appropriate FCM or APNs secrets that belong to the application.
+
+This optional playbook component is only useful to people who develop/build their own Matrix client applications themselves.
+
+
+## Adjusting the playbook configuration
+
+Add the following configuration to your `inventory/host_vars/matrix.DOMAIN/vars.yml` file (adapt to your needs):
+
+```yaml
+matrix_sygnal_enabled: true
+
+# You need at least 1 app defined.
+# The configuration below is incomplete. Read more below.
+matrix_sygnal_apps:
+  com.example.myapp.ios:
+    type: apns
+	keyfile: /data/my_key.p8
+    # .. more configuration ..
+  com.example.myapp.android:
+    type: gcm
+    api_key: your_api_key_for_gcm
+    # .. more configuration ..
+
+matrix_aux_file_definitions:
+  - dest: "{{ matrix_sygnal_data_path }}/my_key.p8"
+    content: |
+      some
+      content
+      here
+    mode: '0600'
+    owner: "{{ matrix_user_username }}"
+    group: "{{ matrix_user_groupname }}"
+```
+
+For a more complete example of available fields and values they can take, see `roles/matrix-sygnal/templates/sygnal.yaml.j2` (or the [upstream `sygnal.yaml.sample` configuration file](https://github.com/matrix-org/sygnal/blob/master/sygnal.yaml.sample)).
+
+Configuring [GCM/FCM](https://firebase.google.com/docs/cloud-messaging/) is easier, as it only requires that you provide some config values.
+
+To configure [APNS](https://developer.apple.com/notifications/) (Apple Push Notification Service), you'd need to provide one or more certificate files.
+To do that, the above example configuration:
+
+- makes use of the `matrix-aux` role (and its `matrix_aux_file_definitions` variable) to make the playbook install files into `/matrix/sygnal/data` (the `matrix_sygnal_data_path` variable). See `roles/matrix-aux/defaults/main.yml` for usage examples. It also makes sure the files are owned by `matrix:matrix`, so that Sygnal can read them. Of course, you can also install these files manually yourself, if you'd rather not use `matrix-aux`.
+
+- references these files in the Sygnal configuration (`matrix_sygnal_apps`) using a path like `/data/..` (the `/matrix/sygnal/data` directory on the host system is mounted into the `/data` directory inside the container)
+
+
+## Installing
+
+Don't forget to add `sygnal.<your-domain>` to DNS as described in [Configuring DNS](configuring-dns.md) before running the playbook.
+
+After configuring the playbook, run the [installation](installing.md) command again:
+
+```
+ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,start
+```
+
+
+## Usage
+
+To make use of your Sygnal installation, you'd need to build your own Matrix client application, which uses the same API keys (for [GCM/FCM](https://firebase.google.com/docs/cloud-messaging/)) and certificates (for [APNS](https://developer.apple.com/notifications/)) and is also pointed to `https://sygnal.DOMAIN` as the configured push server.
+
+Refer to Sygnal's [Notes for application developers](https://github.com/matrix-org/sygnal/blob/master/docs/applications.md) document.