Bring auto-accept invite logic into Synapse (#17147)

This PR ports the logic from the
[synapse_auto_accept_invite](https://github.com/matrix-org/synapse-auto-accept-invite)
module into synapse.

I went with the naive approach of injecting the "module" next to where
third party modules are currently loaded. If there is a better/preferred
way to handle this, I'm all ears. It wasn't obvious to me if there was a
better location to add this logic that would cleanly apply to all
incoming invite events.

Relies on https://github.com/element-hq/synapse/pull/17166 to fix linter
errors.

1 files changed, 29 insertions, 0 deletions

diff --git a/docs/usage/configuration/config_documentation.md b/docs/usage/configuration/config_documentation.md
index e04fdfdfb0..2c917d1f8e 100644
--- a/docs/usage/configuration/config_documentation.md
+++ b/docs/usage/configuration/config_documentation.md
@@ -4595,3 +4595,32 @@ background_updates:
     min_batch_size: 10
     default_batch_size: 50
 ```
+---
+## Auto Accept Invites
+Configuration settings related to automatically accepting invites.
+
+---
+### `auto_accept_invites`
+
+Automatically accepting invites controls whether users are presented with an invite request or if they
+are instead automatically joined to a room when receiving an invite. Set the `enabled` sub-option to true to
+enable auto-accepting invites. Defaults to false.
+This setting has the following sub-options:
+* `enabled`: Whether to run the auto-accept invites logic. Defaults to false.
+* `only_for_direct_messages`: Whether invites should be automatically accepted for all room types, or only
+   for direct messages. Defaults to false.
+* `only_from_local_users`: Whether to only automatically accept invites from users on this homeserver. Defaults to false.
+* `worker_to_run_on`: Which worker to run this module on. This must match the "worker_name".
+
+NOTE: Care should be taken not to enable this setting if the `synapse_auto_accept_invite` module is enabled and installed.
+The two modules will compete to perform the same task and may result in undesired behaviour. For example, multiple join
+events could be generated from a single invite.
+
+Example configuration:
+```yaml
+auto_accept_invites:
+    enabled: true
+    only_for_direct_messages: true
+    only_from_local_users: true
+    worker_to_run_on: "worker_1"
+```