Drop support for delegating email validation (#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

2 files changed, 54 insertions, 112 deletions

diff --git a/synapse/rest/client/account.py b/synapse/rest/client/account.py
index bdc4a9c068..19c2da4244 100644
--- a/synapse/rest/client/account.py
+++ b/synapse/rest/client/account.py
@@ -28,7 +28,6 @@ from synapse.api.errors import (
     SynapseError,
     ThreepidValidationError,
 )
-from synapse.config.emailconfig import ThreepidBehaviour
 from synapse.handlers.ui_auth import UIAuthSessionDataConstants
 from synapse.http.server import HttpServer, finish_request, respond_with_html
 from synapse.http.servlet import (
@@ -64,7 +63,7 @@ class EmailPasswordRequestTokenRestServlet(RestServlet):
         self.config = hs.config
         self.identity_handler = hs.get_identity_handler()
 
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.config.email.can_verify_email:
             self.mailer = Mailer(
                 hs=self.hs,
                 app_name=self.config.email.email_app_name,
@@ -73,11 +72,10 @@ class EmailPasswordRequestTokenRestServlet(RestServlet):
             )
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.OFF:
-            if self.config.email.local_threepid_handling_disabled_due_to_email_config:
-                logger.warning(
-                    "User password resets have been disabled due to lack of email config"
-                )
+        if not self.config.email.can_verify_email:
+            logger.warning(
+                "User password resets have been disabled due to lack of email config"
+            )
             raise SynapseError(
                 400, "Email-based password resets have been disabled on this server"
             )
@@ -129,35 +127,21 @@ class EmailPasswordRequestTokenRestServlet(RestServlet):
 
             raise SynapseError(400, "Email not found", Codes.THREEPID_NOT_FOUND)
 
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.REMOTE:
-            assert self.hs.config.registration.account_threepid_delegate_email
-
-            # Have the configured identity server handle the request
-            ret = await self.identity_handler.requestEmailToken(
-                self.hs.config.registration.account_threepid_delegate_email,
-                email,
-                client_secret,
-                send_attempt,
-                next_link,
-            )
-        else:
-            # Send password reset emails from Synapse
-            sid = await self.identity_handler.send_threepid_validation(
-                email,
-                client_secret,
-                send_attempt,
-                self.mailer.send_password_reset_mail,
-                next_link,
-            )
-
-            # Wrap the session id in a JSON object
-            ret = {"sid": sid}
+        # Send password reset emails from Synapse
+        sid = await self.identity_handler.send_threepid_validation(
+            email,
+            client_secret,
+            send_attempt,
+            self.mailer.send_password_reset_mail,
+            next_link,
+        )
 
         threepid_send_requests.labels(type="email", reason="password_reset").observe(
             send_attempt
         )
 
-        return 200, ret
+        # Wrap the session id in a JSON object
+        return 200, {"sid": sid}
 
 
 class PasswordRestServlet(RestServlet):
@@ -349,7 +333,7 @@ class EmailThreepidRequestTokenRestServlet(RestServlet):
         self.identity_handler = hs.get_identity_handler()
         self.store = self.hs.get_datastores().main
 
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.config.email.can_verify_email:
             self.mailer = Mailer(
                 hs=self.hs,
                 app_name=self.config.email.email_app_name,
@@ -358,11 +342,10 @@ class EmailThreepidRequestTokenRestServlet(RestServlet):
             )
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.OFF:
-            if self.config.email.local_threepid_handling_disabled_due_to_email_config:
-                logger.warning(
-                    "Adding emails have been disabled due to lack of an email config"
-                )
+        if not self.config.email.can_verify_email:
+            logger.warning(
+                "Adding emails have been disabled due to lack of an email config"
+            )
             raise SynapseError(
                 400, "Adding an email to your account is disabled on this server"
             )
@@ -413,35 +396,20 @@ class EmailThreepidRequestTokenRestServlet(RestServlet):
 
             raise SynapseError(400, "Email is already in use", Codes.THREEPID_IN_USE)
 
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.REMOTE:
-            assert self.hs.config.registration.account_threepid_delegate_email
-
-            # Have the configured identity server handle the request
-            ret = await self.identity_handler.requestEmailToken(
-                self.hs.config.registration.account_threepid_delegate_email,
-                email,
-                client_secret,
-                send_attempt,
-                next_link,
-            )
-        else:
-            # Send threepid validation emails from Synapse
-            sid = await self.identity_handler.send_threepid_validation(
-                email,
-                client_secret,
-                send_attempt,
-                self.mailer.send_add_threepid_mail,
-                next_link,
-            )
-
-            # Wrap the session id in a JSON object
-            ret = {"sid": sid}
+        sid = await self.identity_handler.send_threepid_validation(
+            email,
+            client_secret,
+            send_attempt,
+            self.mailer.send_add_threepid_mail,
+            next_link,
+        )
 
         threepid_send_requests.labels(type="email", reason="add_threepid").observe(
             send_attempt
         )
 
-        return 200, ret
+        # Wrap the session id in a JSON object
+        return 200, {"sid": sid}
 
 
 class MsisdnThreepidRequestTokenRestServlet(RestServlet):
@@ -534,25 +502,18 @@ class AddThreepidEmailSubmitTokenServlet(RestServlet):
         self.config = hs.config
         self.clock = hs.get_clock()
         self.store = hs.get_datastores().main
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.config.email.can_verify_email:
             self._failure_email_template = (
                 self.config.email.email_add_threepid_template_failure_html
             )
 
     async def on_GET(self, request: Request) -> None:
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.OFF:
-            if self.config.email.local_threepid_handling_disabled_due_to_email_config:
-                logger.warning(
-                    "Adding emails have been disabled due to lack of an email config"
-                )
-            raise SynapseError(
-                400, "Adding an email to your account is disabled on this server"
+        if not self.config.email.can_verify_email:
+            logger.warning(
+                "Adding emails have been disabled due to lack of an email config"
             )
-        elif self.config.email.threepid_behaviour_email == ThreepidBehaviour.REMOTE:
             raise SynapseError(
-                400,
-                "This homeserver is not validating threepids. Use an identity server "
-                "instead.",
+                400, "Adding an email to your account is disabled on this server"
             )
 
         sid = parse_string(request, "sid", required=True)
diff --git a/synapse/rest/client/register.py b/synapse/rest/client/register.py
index e8e51a9c66..a8402cdb3a 100644
--- a/synapse/rest/client/register.py
+++ b/synapse/rest/client/register.py
@@ -31,7 +31,6 @@ from synapse.api.errors import (
 )
 from synapse.api.ratelimiting import Ratelimiter
 from synapse.config import ConfigError
-from synapse.config.emailconfig import ThreepidBehaviour
 from synapse.config.homeserver import HomeServerConfig
 from synapse.config.ratelimiting import FederationRateLimitConfig
 from synapse.config.server import is_threepid_reserved
@@ -74,7 +73,7 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
         self.identity_handler = hs.get_identity_handler()
         self.config = hs.config
 
-        if self.hs.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.hs.config.email.can_verify_email:
             self.mailer = Mailer(
                 hs=self.hs,
                 app_name=self.config.email.email_app_name,
@@ -83,13 +82,10 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
             )
 
     async def on_POST(self, request: SynapseRequest) -> Tuple[int, JsonDict]:
-        if self.hs.config.email.threepid_behaviour_email == ThreepidBehaviour.OFF:
-            if (
-                self.hs.config.email.local_threepid_handling_disabled_due_to_email_config
-            ):
-                logger.warning(
-                    "Email registration has been disabled due to lack of email config"
-                )
+        if not self.hs.config.email.can_verify_email:
+            logger.warning(
+                "Email registration has been disabled due to lack of email config"
+            )
             raise SynapseError(
                 400, "Email-based registration has been disabled on this server"
             )
@@ -138,35 +134,21 @@ class EmailRegisterRequestTokenRestServlet(RestServlet):
 
             raise SynapseError(400, "Email is already in use", Codes.THREEPID_IN_USE)
 
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.REMOTE:
-            assert self.hs.config.registration.account_threepid_delegate_email
-
-            # Have the configured identity server handle the request
-            ret = await self.identity_handler.requestEmailToken(
-                self.hs.config.registration.account_threepid_delegate_email,
-                email,
-                client_secret,
-                send_attempt,
-                next_link,
-            )
-        else:
-            # Send registration emails from Synapse
-            sid = await self.identity_handler.send_threepid_validation(
-                email,
-                client_secret,
-                send_attempt,
-                self.mailer.send_registration_mail,
-                next_link,
-            )
-
-            # Wrap the session id in a JSON object
-            ret = {"sid": sid}
+        # Send registration emails from Synapse
+        sid = await self.identity_handler.send_threepid_validation(
+            email,
+            client_secret,
+            send_attempt,
+            self.mailer.send_registration_mail,
+            next_link,
+        )
 
         threepid_send_requests.labels(type="email", reason="register").observe(
             send_attempt
         )
 
-        return 200, ret
+        # Wrap the session id in a JSON object
+        return 200, {"sid": sid}
 
 
 class MsisdnRegisterRequestTokenRestServlet(RestServlet):
@@ -260,7 +242,7 @@ class RegistrationSubmitTokenServlet(RestServlet):
         self.clock = hs.get_clock()
         self.store = hs.get_datastores().main
 
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.LOCAL:
+        if self.config.email.can_verify_email:
             self._failure_email_template = (
                 self.config.email.email_registration_template_failure_html
             )
@@ -270,11 +252,10 @@ class RegistrationSubmitTokenServlet(RestServlet):
             raise SynapseError(
                 400, "This medium is currently not supported for registration"
             )
-        if self.config.email.threepid_behaviour_email == ThreepidBehaviour.OFF:
-            if self.config.email.local_threepid_handling_disabled_due_to_email_config:
-                logger.warning(
-                    "User registration via email has been disabled due to lack of email config"
-                )
+        if not self.config.email.can_verify_email:
+            logger.warning(
+                "User registration via email has been disabled due to lack of email config"
+            )
             raise SynapseError(
                 400, "Email-based registration is disabled on this server"
             )