Revert "Drop support for delegating email validation (#13192)" (#13406)

Reverts commit fa71bb18b527d1a3e2629b48640ea67fff2f8c59, and tweaks documentation.

Signed-off-by: 3nprob <git@3n.anonaddy.com>

2 files changed, 50 insertions, 10 deletions

diff --git a/synapse/config/emailconfig.py b/synapse/config/emailconfig.py
index 73b469f414..7765c5b454 100644
--- a/synapse/config/emailconfig.py
+++ b/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 @@ class EmailConfig(Config):
 
         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 @@ class EmailConfig(Config):
                     "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"
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index 685a0423c5..01fb0331bc 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -13,6 +13,7 @@
 # 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
@@ -20,11 +21,15 @@ 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 @@ class RegistrationConfig(Config):
 
         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)