Add a module type for account validity (#9884)

This adds an API for third-party plugin modules to implement account validity, so they can provide this feature instead of Synapse. The module implementing the current behaviour for this feature can be found at https://github.com/matrix-org/synapse-email-account-validity.

To allow for a smooth transition between the current feature and the new module, hooks have been added to the existing account validity endpoints to allow their behaviours to be overridden by a module.

Author: babolivier

changelog.d/9884.feature

@@ -0,0 +1 @@
+Add a module type for the account validity feature.

docs/modules.md

@@ -63,7 +63,7 @@ Modules can register web resources onto Synapse's web server using the following
 API method:
 
 ```python
-def ModuleApi.register_web_resource(path: str, resource: IResource)
+def ModuleApi.register_web_resource(path: str, resource: IResource) -> None
 ```
 
 The path is the full absolute path to register the resource at. For example, if you
@@ -91,12 +91,17 @@ are split in categories. A single module may implement callbacks from multiple c
 and is under no obligation to implement all callbacks from the categories it registers
 callbacks for.
 
+Modules can register callbacks using one of the module API's `register_[...]_callbacks`
+methods. The callback functions are passed to these methods as keyword arguments, with
+the callback name as the argument name and the function as its value. This is demonstrated
+in the example below. A `register_[...]_callbacks` method exists for each module type
+documented in this section.
+
 #### Spam checker callbacks
 
-To register one of the callbacks described in this section, a module needs to use the
-module API's `register_spam_checker_callbacks` method. The callback functions are passed
-to `register_spam_checker_callbacks` as keyword arguments, with the callback name as the
-argument name and the function as its value. This is demonstrated in the example below.
+Spam checker callbacks allow module developers to implement spam mitigation actions for
+Synapse instances. Spam checker callbacks can be registered using the module API's
+`register_spam_checker_callbacks` method.
 
 The available spam checker callbacks are:
 
@@ -115,7 +120,7 @@ async def user_may_invite(inviter: str, invitee: str, room_id: str) -> bool
 
 Called when processing an invitation. The module must return a `bool` indicating whether
 the inviter can invite the invitee to the given room. Both inviter and invitee are
-represented by their Matrix user ID (i.e. `@alice:example.com`).
+represented by their Matrix user ID (e.g. `@alice:example.com`).
 
 ```python
 async def user_may_create_room(user: str) -> bool
@@ -188,6 +193,36 @@ async def check_media_file_for_spam(
 Called when storing a local or remote file. The module must return a boolean indicating
 whether the given file can be stored in the homeserver's media store.
 
+#### Account validity callbacks
+
+Account validity callbacks allow module developers to add extra steps to verify the
+validity on an account, i.e. see if a user can be granted access to their account on the
+Synapse instance. Account validity callbacks can be registered using the module API's
+`register_account_validity_callbacks` method.
+
+The available account validity callbacks are:
+
+```python
+async def is_user_expired(user: str) -> Optional[bool]
+```
+
+Called when processing any authenticated request (except for logout requests). The module
+can return a `bool` to indicate whether the user has expired and should be locked out of
+their account, or `None` if the module wasn't able to figure it out. The user is
+represented by their Matrix user ID (e.g. `@alice:example.com`).
+
+If the module returns `True`, the current request will be denied with the error code
+`ORG_MATRIX_EXPIRED_ACCOUNT` and the HTTP status code 403. Note that this doesn't
+invalidate the user's access token.
+
+```python
+async def on_user_registration(user: str) -> None
+```
+
+Called after successfully registering a user, in case the module needs to perform extra
+operations to keep track of them. (e.g. add them to a database table). The user is
+represented by their Matrix user ID.
+
 ### Porting an existing module that uses the old interface
 
 In order to port a module that uses Synapse's old module interface, its author needs to:

docs/sample_config.yaml

@@ -1310,91 +1310,6 @@ account_threepid_delegates:
 #auto_join_rooms_for_guests: false
 
 
-## Account Validity ##
-
-# Optional account validity configuration. This allows for accounts to be denied
-# any request after a given period.
-#
-# Once this feature is enabled, Synapse will look for registered users without an
-# expiration date at startup and will add one to every account it found using the
-# current settings at that time.
-# This means that, if a validity period is set, and Synapse is restarted (it will
-# then derive an expiration date from the current validity period), and some time
-# after that the validity period changes and Synapse is restarted, the users'
-# expiration dates won't be updated unless their account is manually renewed. This
-# date will be randomly selected within a range [now + period - d ; now + period],
-# where d is equal to 10% of the validity period.
-#
-account_validity:
-  # The account validity feature is disabled by default. Uncomment the
-  # following line to enable it.
-  #
-  #enabled: true
-
-  # The period after which an account is valid after its registration. When
-  # renewing the account, its validity period will be extended by this amount
-  # of time. This parameter is required when using the account validity
-  # feature.
-  #
-  #period: 6w
-
-  # The amount of time before an account's expiry date at which Synapse will
-  # send an email to the account's email address with a renewal link. By
-  # default, no such emails are sent.
-  #
-  # If you enable this setting, you will also need to fill out the 'email' and
-  # 'public_baseurl' configuration sections.
-  #
-  #renew_at: 1w
-
-  # The subject of the email sent out with the renewal link. '%(app)s' can be
-  # used as a placeholder for the 'app_name' parameter from the 'email'
-  # section.
-  #
-  # Note that the placeholder must be written '%(app)s', including the
-  # trailing 's'.
-  #
-  # If this is not set, a default value is used.
-  #
-  #renew_email_subject: "Renew your %(app)s account"
-
-  # Directory in which Synapse will try to find templates for the HTML files to
-  # serve to the user when trying to renew an account. If not set, default
-  # templates from within the Synapse package will be used.
-  #
-  # The currently available templates are:
-  #
-  # * account_renewed.html: Displayed to the user after they have successfully
-  #       renewed their account.
-  #
-  # * account_previously_renewed.html: Displayed to the user if they attempt to
-  #       renew their account with a token that is valid, but that has already
-  #       been used. In this case the account is not renewed again.
-  #
-  # * invalid_token.html: Displayed to the user when they try to renew an account
-  #       with an unknown or invalid renewal token.
-  #
-  # See https://github.com/matrix-org/synapse/tree/master/synapse/res/templates for
-  # default template contents.
-  #
-  # The file name of some of these templates can be configured below for legacy
-  # reasons.
-  #
-  #template_dir: "res/templates"
-
-  # A custom file name for the 'account_renewed.html' template.
-  #
-  # If not set, the file is assumed to be named "account_renewed.html".
-  #
-  #account_renewed_html_path: "account_renewed.html"
-
-  # A custom file name for the 'invalid_token.html' template.
-  #
-  # If not set, the file is assumed to be named "invalid_token.html".
-  #
-  #invalid_token_html_path: "invalid_token.html"
-
-
 ## Metrics ###
 
 # Enable collection and rendering of performance metrics

synapse/api/auth.py

@@ -62,16 +62,14 @@ def __init__(self, hs: "HomeServer"):
         self.clock = hs.get_clock()
         self.store = hs.get_datastore()
         self.state = hs.get_state_handler()
+        self._account_validity_handler = hs.get_account_validity_handler()
 
         self.token_cache: LruCache[str, Tuple[str, bool]] = LruCache(
             10000, "token_cache"
         )
 
         self._auth_blocking = AuthBlocking(self.hs)
 
-        self._account_validity_enabled = (
-            hs.config.account_validity.account_validity_enabled
-        )
         self._track_appservice_user_ips = hs.config.track_appservice_user_ips
         self._macaroon_secret_key = hs.config.macaroon_secret_key
         self._force_tracing_for_users = hs.config.tracing.force_tracing_for_users
@@ -187,12 +185,17 @@ async def get_user_by_req(
             shadow_banned = user_info.shadow_banned
 
             # Deny the request if the user account has expired.
-            if self._account_validity_enabled and not allow_expired:
-                if await self.store.is_account_expired(
-                    user_info.user_id, self.clock.time_msec()
+            if not allow_expired:
+                if await self._account_validity_handler.is_user_expired(
+                    user_info.user_id
                 ):
+                    # Raise the error if either an account validity module has determined
+                    # the account has expired, or the legacy account validity
+                    # implementation is enabled and determined the account has expired
                     raise AuthError(
-                        403, "User account has expired", errcode=Codes.EXPIRED_ACCOUNT
+                        403,
+                        "User account has expired",
+                        errcode=Codes.EXPIRED_ACCOUNT,
                     )
 
             device_id = user_info.device_id

synapse/config/account_validity.py

@@ -18,6 +18,21 @@ class AccountValidityConfig(Config):
     section = "account_validity"
 
     def read_config(self, config, **kwargs):
+        """Parses the old account validity config. The config format looks like this:
+
+        account_validity:
+            enabled: true
+            period: 6w
+            renew_at: 1w
+            renew_email_subject: "Renew your %(app)s account"
+            template_dir: "res/templates"
+            account_renewed_html_path: "account_renewed.html"
+            invalid_token_html_path: "invalid_token.html"
+
+        We expect admins to use modules for this feature (which is why it doesn't appear
+        in the sample config file), but we want to keep support for it around for a bit
+        for backwards compatibility.
+        """
         account_validity_config = config.get("account_validity") or {}
         self.account_validity_enabled = account_validity_config.get("enabled", False)
         self.account_validity_renew_by_email_enabled = (
@@ -75,90 +90,3 @@ def read_config(self, config, **kwargs):
             ],
             account_validity_template_dir,
         )
-
-    def generate_config_section(self, **kwargs):
-        return """\
-        ## Account Validity ##
-
-        # Optional account validity configuration. This allows for accounts to be denied
-        # any request after a given period.
-        #
-        # Once this feature is enabled, Synapse will look for registered users without an
-        # expiration date at startup and will add one to every account it found using the
-        # current settings at that time.
-        # This means that, if a validity period is set, and Synapse is restarted (it will
-        # then derive an expiration date from the current validity period), and some time
-        # after that the validity period changes and Synapse is restarted, the users'
-        # expiration dates won't be updated unless their account is manually renewed. This
-        # date will be randomly selected within a range [now + period - d ; now + period],
-        # where d is equal to 10% of the validity period.
-        #
-        account_validity:
-          # The account validity feature is disabled by default. Uncomment the
-          # following line to enable it.
-          #
-          #enabled: true
-
-          # The period after which an account is valid after its registration. When
-          # renewing the account, its validity period will be extended by this amount
-          # of time. This parameter is required when using the account validity
-          # feature.
-          #
-          #period: 6w
-
-          # The amount of time before an account's expiry date at which Synapse will
-          # send an email to the account's email address with a renewal link. By
-          # default, no such emails are sent.
-          #
-          # If you enable this setting, you will also need to fill out the 'email' and
-          # 'public_baseurl' configuration sections.
-          #
-          #renew_at: 1w
-
-          # The subject of the email sent out with the renewal link. '%(app)s' can be
-          # used as a placeholder for the 'app_name' parameter from the 'email'
-          # section.
-          #
-          # Note that the placeholder must be written '%(app)s', including the
-          # trailing 's'.
-          #
-          # If this is not set, a default value is used.
-          #
-          #renew_email_subject: "Renew your %(app)s account"
-
-          # Directory in which Synapse will try to find templates for the HTML files to
-          # serve to the user when trying to renew an account. If not set, default
-          # templates from within the Synapse package will be used.
-          #
-          # The currently available templates are:
-          #
-          # * account_renewed.html: Displayed to the user after they have successfully
-          #       renewed their account.
-          #
-          # * account_previously_renewed.html: Displayed to the user if they attempt to
-          #       renew their account with a token that is valid, but that has already
-          #       been used. In this case the account is not renewed again.
-          #
-          # * invalid_token.html: Displayed to the user when they try to renew an account
-          #       with an unknown or invalid renewal token.
-          #
-          # See https://github.com/matrix-org/synapse/tree/master/synapse/res/templates for
-          # default template contents.
-          #
-          # The file name of some of these templates can be configured below for legacy
-          # reasons.
-          #
-          #template_dir: "res/templates"
-
-          # A custom file name for the 'account_renewed.html' template.
-          #
-          # If not set, the file is assumed to be named "account_renewed.html".
-          #
-          #account_renewed_html_path: "account_renewed.html"
-
-          # A custom file name for the 'invalid_token.html' template.
-          #
-          # If not set, the file is assumed to be named "invalid_token.html".
-          #
-          #invalid_token_html_path: "invalid_token.html"
-        """