Well, `config.yaml` has been playbook-managed for a long time.
It's now extended to match the default sample config of the Discord
bridge.

With this patch, we also make `registration.yaml` playbook-managed,
which leads us to consistency with all other bridges.

Along with that, we introduce `./config` and `./data` separation,
like we do for the other bridges.

According to
https://passlib.readthedocs.io/en/stable/lib/passlib.hash.sha512_crypt.html:

> salt (str) – Optional salt string. If not specified, one will be autogenerated (this is recommended).
> If specified, it must be 0-16 characters, drawn from the regexp range [./0-9A-Za-z].

Until now, we were using invalid characters (like `-`). We were also
going over the requested length limit of 16 characters.

This is most likely what was causing `ValueError` exceptions for some people,
as reported in #209 (Github Issue).
Ansible's source code (`lib/ansible/utils/encrypt.py`) shows that Ansible tries
to use passlib if available and falls back to Python's `crypt` module if not.
For Mac, `crypt.crypt` doesn't seem to work, so Ansible always requires passlib.

Looks like crypt is forgiving when length or character requirements are
not obeyed. It would auto-trim a salt string to make it work, which means
that we could end up with the same hash if we call it with salts which aer only
different after their 16th character.

For these reasons (crypt autotriming and passlib downright complaining),
we're now using shorter and more diverse salts.

- following spantaleev transition of the telegram brigde
- adding a validate_config task

I've not found this welcome bot to work at all in my previous attempts.
It would simply not reply, even though federation works.

It seems like this is also a potential privacy issue, as per
https://gist.github.com/maxidorius/5736fd09c9194b7a6dc03b6b8d7220d0

Related to #193, but for the Facebook bridge.
(other bridges can be changed to do the same later).

This patch makes the bridge configuration entirely managed by the
Ansible playbook. The bridge's `config.yaml` and `registration.yaml`
configuration files are regenerated every time the playbook runs.

This allows us to apply updates to those files and to avoid
people having to manage the configuration files manually on the server.

-------------------------------------------------------------

A deficiency of the current approach to dumping YAML configuration in
`config.yaml` is that we strip all comments from it.
Later on, when the bridge actually starts, it will load and redump
(this time with comments), which will make the `config.yaml` file
change.

Subsequent playbook runs will report "changed" for the
"Ensure mautrix-facebook config.yaml installed" task, which is a little
strange.

We might wish to improve this in the future, if possible.

Still, it's better to have a (usually) somewhat meaningless "changed"
task than to what we had -- never rebuilding the configuration.

From what I see, this was never implemented to begin with.

Fixes #189 (Github Issue).

Fixes #171 (Github Issue).

The goal is to move each bridge into its own separate role.
This commit starts off the work on this with 2 bridges:
- mautrix-telegram
- mautrix-whatsapp

Each bridge's role (including these 2) is meant to:

- depend only on the matrix-base role

- integrate nicely with the matrix-synapse role (if available)

- integrate nicely with the matrix-nginx-proxy role (if available and if
required). mautrix-telegram bridge benefits from integrating with
it.

- not break if matrix-synapse or matrix-nginx-proxy are not used at all

This has been provoked by #174 (Github Issue).

By default, `--tags=self-check` no longer validates certificates
when `matrix_ssl_retrieval_method` is set to `self-signed`.

Besides this default, people can also enable/disable validation using the
individual role variables manually.

Fixes #124 (Github Issue)

Most (all?) of our Matrix services are running in the `matrix` network,
so they were safe -- not accessible from Coturn to begin with.

Isolating Coturn into its own network is a security improvement
for people who were starting other services in the default
Docker network. Those services were potentially reachable over the
private Docker network from Coturn.

Discussed in #120 (Github Pull Request)

This is more explicit than hiding it in the role defaults.

People who reuse the roles in their own playbook (and not only) may
incorrectly define `ansible_host` to be a hostname or some local address.

Making it more explicit is more likely to prevent such mistakes.

Related to #105 (Github Pull Request).

Bridge is setup to work on the matrix side with this, but the discord invite link is not automatically generated.

`matrix_synapse_no_tls` is now implicit, so we've gotten rid of it.

The `homeserver.yaml.j2` template has been synchronized with the
configuration generated by Synapse v0.99.1 (some new options
are present, etc.)

This makes all containers (except mautrix-telegram and
mautrix-whatsapp), start as a non-root user.

We do this, because we don't trust some of the images.
In any case, we'd rather not trust ALL images and avoid giving
`root` access at all. We can't be sure they would drop privileges
or what they might do before they do it.

Because Postfix doesn't support running as non-root,
it had to be replaced by an Exim mail server.

The matrix-nginx-proxy nginx container image is patched up
(by replacing its main configuration) so that it can work as non-root.
It seems like there's no other good image that we can use and that is up-to-date
(https://hub.docker.com/r/nginxinc/nginx-unprivileged is outdated).

Likewise for riot-web (https://hub.docker.com/r/bubuntux/riot-web/),
we patch it up ourselves when starting (replacing the main nginx
configuration).
Ideally, it would be fixed upstream so we can simplify.

It worked without it too, but doing this is more consistent with the
mxisd recommendations.

Implements #77 (Github issue).

The matrix-nginx-proxy role can now be used independently.
This makes it consistent with all other roles, with
the `matrix-base` role remaining as their only dependency.

Separating matrix-nginx-proxy was relatively straightforward, with
the exception of the Mautrix Telegram reverse-proxying configuration.
Mautrix Telegram, being an extension/bridge, does not feel important enough
to justify its own special handling in matrix-nginx-proxy.

Thus, we've introduced the concept of "additional configuration blocks"
(`matrix_nginx_proxy_proxy_matrix_additional_server_configuration_blocks`),
where any module can register its own custom nginx server blocks.

For such dynamic registration to work, the order of role execution
becomes important. To make it possible for each module participating
in dynamic registration to verify that the order of execution is
correct, we've also introduced a `matrix_nginx_proxy_role_executed`
variable.

It should be noted that this doesn't make the matrix-synapse role
dependent on matrix-nginx-proxy. It's optional runtime detection
and registration, and it only happens in the matrix-synapse role
when `matrix_mautrix_telegram_enabled: true`.