Add documentation for new module api callback methods

Author: anoadragon453

docs/modules/third_party_rules_callbacks.md

@@ -265,6 +265,44 @@ server_.
 
 If multiple modules implement this callback, Synapse runs them all in order.
 
+### `on_add_user_third_party_identifier`
+
+_First introduced in Synapse v1.78.0_
+
+```python
+async def on_add_user_third_party_identifier(user_id: str, medium: str, address: str) -> None:
+```
+
+Called just before creating an association between a user and a third-party identifier
+(email address, phone number). The module is given the Matrix ID of the user the
+association is for, as well as the medium (`email` or `msisdn`) and address of the
+third-party identifier (i.e. an email address).
+
+Note that this callback is _not_ called if a user attempts to bind their third-party identifier
+to an identity server (via a call to [`POST
+/_matrix/client/v3/account/3pid/bind`](https://spec.matrix.org/v1.5/client-server-api/#post_matrixclientv3account3pidbind)).
+
+If multiple modules implement this callback, Synapse runs them all in order.
+
+### `on_remove_user_third_party_identifier`
+
+_First introduced in Synapse v1.78.0_
+
+```python
+async def on_remove_user_third_party_identifier(user_id: str, medium: str, address: str) -> None:
+```
+
+Called just before removing an association between a user and a third-party identifier
+(email address, phone number). The module is given the Matrix ID of the user the
+association is for, as well as the medium (`email` or `msisdn`) and address of the
+third-party identifier (i.e. an email address).
+
+Note that this callback is _not_ called if a user attempts to unbind their third-party
+identifier from an identity server (via a call to [`POST
+/_matrix/client/v3/account/3pid/unbind`](https://spec.matrix.org/v1.5/client-server-api/#post_matrixclientv3account3pidunbind)).
+
+If multiple modules implement this callback, Synapse runs them all in order.
+
 ## Example
 
 The example below is a module that implements the third-party rules callback
@@ -297,4 +335,4 @@ class EventCensorer:
         )
         event_dict["content"] = new_event_content
         return event_dict
-```
+```

docs/upgrade.md

@@ -97,6 +97,32 @@ admin API with an identical endpoint at `/_synapse/admin/v1/media/delete`. Pleas
 update your tooling to use the new endpoint. The deprecated version will be removed
 in a future release.
 
+## The `on_threepid_bind` module callback method has been deprecated
+
+The [`on_threepid_bind`](modules/third_party_rules_callbacks.md#on_threepid_bind) "third-party rules"
+Synapse module callback method has been deprecated
+in favour of a new module method,
+[`on_add_user_third_party_identifier`](modules/third_party_rules_callbacks.md#on_add_user_third_party_identifier).
+`on_threepid_bind` will be removed in a future version of Synapse. You should check whether any Synapse
+modules in use in your deployment are making use of `on_threepid_bind`, and update them where possible.
+
+The arguments and functionality of the new method are nearly the same; `on_threepid_bind` was called
+directly *after* a user adds a third-party identifier (email, phone number) to their account, while
+`on_add_user_third_party_identifier` is called just *before* a user adds a third-party identifier.
+
+The justification behind the swap in logical ordering is that `on_add_user_third_party_identifier`
+may be extended in the future to allow blocking a user from adding a third-party identifier to their
+account. The reason behind the name change is that the old method's name, `on_threepid_bind`, was
+misleading. A user is considered to "bind" their third-party ID to their Matrix ID only if they
+do so via an [identity server](https://spec.matrix.org/latest/identity-service-api/)
+(so that users on other homeservers may find them). But this method was not called in that case -
+it was only called when a user added a third-party identifier on the local homeserver.
+
+Module developers may also be interested in the related
+[`on_remove_user_third_party_identifier`](modules/third_party_rules_callbacks.md#on_remove_user_third_party_identifier)
+module callback method that was also added in Synapse v1.77.0. This new method is called when a
+user removes a third-party identifier from their account.
+
 # Upgrading to v1.76.0
 
 ## Faster joins are enabled by default