Revert "Drop support for delegating email validation (#13192)"

changelog.d/13406.misc

@@ -0,0 +1 @@
+Warn instead of error when using `account_threepid_delegates.email`, which was deprecated in 1.64.0rc1.

docs/upgrade.md

@@ -91,19 +91,6 @@ process, for example:
 
 # 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.
-
 ## Changes to the event replication streams
 
 Synapse now includes a flag indicating if an event is an outlier when

synapse/app/homeserver.py

@@ -44,6 +44,7 @@
     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
@@ -201,7 +202,7 @@ def _configure_named_resource(
                 }
             )
 
-            if self.config.email.can_verify_email:
+            if self.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
                 from synapse.rest.synapse.client.password_reset import (
                     PasswordResetSubmitTokenResource,
                 )

synapse/config/emailconfig.py

@@ -18,6 +18,7 @@
 import email.utils
 import logging
 import os
+from enum import Enum
 from typing import Any
 
 import attr
@@ -135,22 +136,40 @@ 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" '
-                "is no longer supported. Please remove it from the config file."
+                'The config option "trust_identity_server_for_password_resets" has been removed.'
+                "Please consult the configuration manual at docs/usage/configuration/config_documentation.md for "
+                "details and update your config file."
             )
 
-        # If we have email config settings, assume that we can verify ownership of
-        # email addresses.
-        self.can_verify_email = email_config != {}
+        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
 
         # 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.can_verify_email:
+        if self.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
             missing = []
             if not self.email_notif_from:
                 missing.append("email.notif_from")
@@ -341,3 +360,18 @@ 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

@@ -13,18 +13,23 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import argparse
+import logging
 from typing import Any, Optional
 
 from synapse.api.constants import RoomCreationPreset
 from synapse.config._base import Config, ConfigError
 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
+logger = logging.getLogger(__name__)
+
+LEGACY_EMAIL_DELEGATE_WARNING = """\
+Delegation of email verification to an identity server is now deprecated. 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`.
+
+This will be an error in a future version.
 """
 
 
@@ -59,8 +64,9 @@ def read_config(self, config: JsonDict, **kwargs: Any) -> None:
 
         account_threepid_delegates = config.get("account_threepid_delegates") or {}
         if "email" in account_threepid_delegates:
-            raise ConfigError(NO_EMAIL_DELEGATE_ERROR)
-        # self.account_threepid_delegate_email = account_threepid_delegates.get("email")
+            logger.warning(LEGACY_EMAIL_DELEGATE_WARNING)
+
+        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

@@ -26,6 +26,7 @@
     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
@@ -415,6 +416,48 @@ async def send_threepid_validation(
 
         return session_id
 
+    async def request_email_token(
+        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,
@@ -488,7 +531,18 @@ async def validate_threepid_session(
         validation_session = None
 
         # Try to validate as email
-        if self.hs.config.email.can_verify_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:
             # 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

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