Drop support for delegating email validation (matrix-org#13192)

* Drop support for delegating email validation

Delegating email validation to an IS is insecure (since it allows the owner of
the IS to do a password reset on your HS), and has long been deprecated. It
will now cause a config error at startup.

* Update unit test which checks for email verification

Give it an `email` config instead of a threepid delegate

* Remove unused method `requestEmailToken`

* Simplify config handling for email verification

Rather than an enum and a boolean, all we need here is a single bool, which
says whether we are or are not doing email verification.

* update docs

* changelog

* upgrade.md: fix typo

* update version number

this will be in 1.64, not 1.63

* update version number

this one too

Author: richvdh

CHANGES.md

@@ -1,3 +1,8 @@
+Synapse vNext
+=============
+
+As of this release, Synapse no longer allows the tasks of verifying email address ownership, and password reset confirmation, to be delegated to an identity server. For more information, see the [upgrade notes](https://github.com/matrix-org/synapse/blob/release-v1.63/docs/upgrade.md#upgrading-to-v1630).
+
 Synapse 1.63.0rc1 (2022-07-12)
 ==============================
 
@@ -73,15 +78,13 @@ Internal Changes
 - More aggressively rotate push actions. ([\#13211](https://github.com/matrix-org/synapse/issues/13211))
 - Add `max_line_length` setting for Python files to the `.editorconfig`. Contributed by @sumnerevans @ Beeper. ([\#13228](https://github.com/matrix-org/synapse/issues/13228))
 
-
 Synapse 1.62.0 (2022-07-05)
 ===========================
 
 No significant changes since 1.62.0rc3.
 
 Authors of spam-checker plugins should consult the [upgrade notes](https://github.com/matrix-org/synapse/blob/release-v1.62/docs/upgrade.md#upgrading-to-v1620) to learn about the enriched signatures for spam checker callbacks, which are supported with this release of Synapse.
 
-
 Synapse 1.62.0rc3 (2022-07-04)
 ==============================
 

changelog.d/13192.removal

@@ -0,0 +1 @@
+Drop support for delegating email verification to an external server.

docs/upgrade.md

@@ -89,6 +89,21 @@ process, for example:
     dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
     ```
 
+# Upgrading to v1.64.0
+
+## Delegation of email validation no longer supported
+
+As of this version, Synapse no longer allows the tasks of verifying email address
+ownership, and password reset confirmation, to be delegated to an identity server.
+
+To continue to allow users to add email addresses to their homeserver accounts,
+and perform password resets, make sure that Synapse is configured with a
+working email server in the `email` configuration section (including, at a
+minimum, a `notif_from` setting.)
+
+Specifying an `email` setting under `account_threepid_delegates` will now cause
+an error at startup.
+
 # Upgrading to v1.62.0
 
 ## New signatures for spam checker callbacks

docs/usage/configuration/config_documentation.md

@@ -2168,30 +2168,26 @@ default_identity_server: https://matrix.org
 ---
 ### `account_threepid_delegates`
 
-Handle threepid (email/phone etc) registration and password resets through a set of
-*trusted* identity servers. Note that this allows the configured identity server to
-reset passwords for accounts!
+Delegate verification of phone numbers to an identity server.
 
-Be aware that if `email` is not set, and SMTP options have not been
-configured in the email config block, registration and user password resets via
-email will be globally disabled.
+When a user wishes to add a phone number to their account, we need to verify that they
+actually own that phone number, which requires sending them a text message (SMS).
+Currently Synapse does not support sending those texts itself and instead delegates the
+task to an identity server. The base URI for the identity server to be used is
+specified by the `account_threepid_delegates.msisdn` option.
 
-Additionally, if `msisdn` is not set, registration and password resets via msisdn
-will be disabled regardless, and users will not be able to associate an msisdn
-identifier to their account. This is due to Synapse currently not supporting
-any method of sending SMS messages on its own.
+If this is left unspecified, Synapse will not allow users to add phone numbers to
+their account.
 
-To enable using an identity server for operations regarding a particular third-party
-identifier type, set the value to the URL of that identity server as shown in the
-examples below.
+(Servers handling the these requests must answer the `/requestToken` endpoints defined
+by the Matrix Identity Service API
+[specification](https://matrix.org/docs/spec/identity_service/latest).)
 
-Servers handling the these requests must answer the `/requestToken` endpoints defined
-by the Matrix Identity Service API [specification](https://matrix.org/docs/spec/identity_service/latest).
+*Updated in Synapse 1.64.0*: No longer accepts an `email` option.
 
 Example configuration:
 ```yaml
 account_threepid_delegates:
-    email: https://example.com     # Delegate email sending to example.com
     msisdn: http://localhost:8090  # Delegate SMS sending to this local process
 ```
 ---

synapse/app/homeserver.py

@@ -44,7 +44,6 @@
     register_start,
 )
 from synapse.config._base import ConfigError, format_config_error
-from synapse.config.emailconfig import ThreepidBehaviour
 from synapse.config.homeserver import HomeServerConfig
 from synapse.config.server import ListenerConfig
 from synapse.federation.transport.server import TransportLayerServer
@@ -202,7 +201,7 @@ def _configure_named_resource(
                 }
             )
 
-            if self.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+            if self.config.email.can_verify_email:
                 from synapse.rest.synapse.client.password_reset import (
                     PasswordResetSubmitTokenResource,
                 )

synapse/config/emailconfig.py

@@ -18,7 +18,6 @@
 import email.utils
 import logging
 import os
-from enum import Enum
 from typing import Any
 
 import attr
@@ -131,41 +130,22 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
 
         self.email_enable_notifs = email_config.get("enable_notifs", False)
 
-        self.threepid_behaviour_email = (
-            # Have Synapse handle the email sending if account_threepid_delegates.email
-            # is not defined
-            # msisdn is currently always remote while Synapse does not support any method of
-            # sending SMS messages
-            ThreepidBehaviour.REMOTE
-            if self.root.registration.account_threepid_delegate_email
-            else ThreepidBehaviour.LOCAL
-        )
-
         if config.get("trust_identity_server_for_password_resets"):
             raise ConfigError(
                 'The config option "trust_identity_server_for_password_resets" '
-                'has been replaced by "account_threepid_delegate". '
-                "Please consult the configuration manual at docs/usage/configuration/config_documentation.md for "
-                "details and update your config file."
+                "is no longer supported. Please remove it from the config file."
             )
 
-        self.local_threepid_handling_disabled_due_to_email_config = False
-        if (
-            self.threepid_behaviour_email == ThreepidBehaviour.LOCAL
-            and email_config == {}
-        ):
-            # We cannot warn the user this has happened here
-            # Instead do so when a user attempts to reset their password
-            self.local_threepid_handling_disabled_due_to_email_config = True
-
-            self.threepid_behaviour_email = ThreepidBehaviour.OFF
+        # If we have email config settings, assume that we can verify ownership of
+        # email addresses.
+        self.can_verify_email = email_config != {}
 
         # Get lifetime of a validation token in milliseconds
         self.email_validation_token_lifetime = self.parse_duration(
             email_config.get("validation_token_lifetime", "1h")
         )
 
-        if self.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.can_verify_email:
             missing = []
             if not self.email_notif_from:
                 missing.append("email.notif_from")
@@ -356,18 +336,3 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
                     "Config option email.invite_client_location must be a http or https URL",
                     path=("email", "invite_client_location"),
                 )
-
-
-class ThreepidBehaviour(Enum):
-    """
-    Enum to define the behaviour of Synapse with regards to when it contacts an identity
-    server for 3pid registration and password resets
-
-    REMOTE = use an external server to send tokens
-    LOCAL = send tokens ourselves
-    OFF = disable registration via 3pid and password resets
-    """
-
-    REMOTE = "remote"
-    LOCAL = "local"
-    OFF = "off"

synapse/config/registration.py

@@ -20,6 +20,13 @@
 from synapse.types import JsonDict, RoomAlias, UserID
 from synapse.util.stringutils import random_string_with_symbols, strtobool
 
+NO_EMAIL_DELEGATE_ERROR = """\
+Delegation of email verification to an identity server is no longer supported. To
+continue to allow users to add email addresses to their accounts, and use them for
+password resets, configure Synapse with an SMTP server via the `email` setting, and
+remove `account_threepid_delegates.email`.
+"""
+
 
 class RegistrationConfig(Config):
     section = "registration"
@@ -51,7 +58,9 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
         self.bcrypt_rounds = config.get("bcrypt_rounds", 12)
 
         account_threepid_delegates = config.get("account_threepid_delegates") or {}
-        self.account_threepid_delegate_email = account_threepid_delegates.get("email")
+        if "email" in account_threepid_delegates:
+            raise ConfigError(NO_EMAIL_DELEGATE_ERROR)
+        # self.account_threepid_delegate_email = account_threepid_delegates.get("email")
         self.account_threepid_delegate_msisdn = account_threepid_delegates.get("msisdn")
         self.default_identity_server = config.get("default_identity_server")
         self.allow_guest_access = config.get("allow_guest_access", False)

synapse/handlers/identity.py

@@ -26,7 +26,6 @@
     SynapseError,
 )
 from synapse.api.ratelimiting import Ratelimiter
-from synapse.config.emailconfig import ThreepidBehaviour
 from synapse.http import RequestTimedOutError
 from synapse.http.client import SimpleHttpClient
 from synapse.http.site import SynapseRequest
@@ -434,48 +433,6 @@ async def send_threepid_validation(
 
         return session_id
 
-    async def requestEmailToken(
-        self,
-        id_server: str,
-        email: str,
-        client_secret: str,
-        send_attempt: int,
-        next_link: Optional[str] = None,
-    ) -> JsonDict:
-        """
-        Request an external server send an email on our behalf for the purposes of threepid
-        validation.
-
-        Args:
-            id_server: The identity server to proxy to
-            email: The email to send the message to
-            client_secret: The unique client_secret sends by the user
-            send_attempt: Which attempt this is
-            next_link: A link to redirect the user to once they submit the token
-
-        Returns:
-            The json response body from the server
-        """
-        params = {
-            "email": email,
-            "client_secret": client_secret,
-            "send_attempt": send_attempt,
-        }
-        if next_link:
-            params["next_link"] = next_link
-
-        try:
-            data = await self.http_client.post_json_get_json(
-                id_server + "/_matrix/identity/api/v1/validate/email/requestToken",
-                params,
-            )
-            return data
-        except HttpResponseException as e:
-            logger.info("Proxied requestToken failed: %r", e)
-            raise e.to_synapse_error()
-        except RequestTimedOutError:
-            raise SynapseError(500, "Timed out contacting identity server")
-
     async def requestMsisdnToken(
         self,
         id_server: str,
@@ -549,18 +506,7 @@ async def validate_threepid_session(
         validation_session = None
 
         # Try to validate as email
-        if self.hs.config.email.threepid_behaviour_email == ThreepidBehaviour.REMOTE:
-            # Remote emails will only be used if a valid identity server is provided.
-            assert (
-                self.hs.config.registration.account_threepid_delegate_email is not None
-            )
-
-            # Ask our delegated email identity server
-            validation_session = await self.threepid_from_creds(
-                self.hs.config.registration.account_threepid_delegate_email,
-                threepid_creds,
-            )
-        elif self.hs.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.hs.config.email.can_verify_email:
             # Get a validated session matching these details
             validation_session = await self.store.get_threepid_validation_session(
                 "email", client_secret, sid=sid, validated=True

synapse/handlers/ui_auth/checkers.py

@@ -19,7 +19,6 @@
 
 from synapse.api.constants import LoginType
 from synapse.api.errors import Codes, LoginError, SynapseError
-from synapse.config.emailconfig import ThreepidBehaviour
 from synapse.util import json_decoder
 
 if TYPE_CHECKING:
@@ -153,7 +152,7 @@ async def _check_threepid(self, medium: str, authdict: dict) -> dict:
 
         logger.info("Getting validated threepid. threepidcreds: %r", (threepid_creds,))
 
-        # msisdns are currently always ThreepidBehaviour.REMOTE
+        # msisdns are currently always verified via the IS
         if medium == "msisdn":
             if not self.hs.config.registration.account_threepid_delegate_msisdn:
                 raise SynapseError(
@@ -164,18 +163,7 @@ async def _check_threepid(self, medium: str, authdict: dict) -> dict:
                 threepid_creds,
             )
         elif medium == "email":
-            if (
-                self.hs.config.email.threepid_behaviour_email
-                == ThreepidBehaviour.REMOTE
-            ):
-                assert self.hs.config.registration.account_threepid_delegate_email
-                threepid = await identity_handler.threepid_from_creds(
-                    self.hs.config.registration.account_threepid_delegate_email,
-                    threepid_creds,
-                )
-            elif (
-                self.hs.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL
-            ):
+            if self.hs.config.email.can_verify_email:
                 threepid = None
                 row = await self.store.get_threepid_validation_session(
                     medium,
@@ -227,10 +215,7 @@ def __init__(self, hs: "HomeServer"):
         _BaseThreepidAuthChecker.__init__(self, hs)
 
     def is_enabled(self) -> bool:
-        return self.hs.config.email.threepid_behaviour_email in (
-            ThreepidBehaviour.REMOTE,
-            ThreepidBehaviour.LOCAL,
-        )
+        return self.hs.config.email.can_verify_email
 
     async def check_auth(self, authdict: dict, clientip: str) -> Any:
         return await self._check_threepid("email", authdict)