Allow password providers to bind emails (#4947)

This PR allows password provider modules to bind email addresses when a user is registering and is motivated by matrix-org/matrix-synapse-ldap3#58

synapse/handlers/register.py

@@ -153,6 +153,7 @@ class RegistrationHandler(BaseHandler):
         user_type=None,
         default_display_name=None,
         address=None,
+        bind_emails=[],
     ):
         """Registers a new client on the server.
 
@@ -172,6 +173,7 @@ class RegistrationHandler(BaseHandler):
             default_display_name (unicode|None): if set, the new user's displayname
               will be set to this. Defaults to 'localpart'.
             address (str|None): the IP address used to perform the registration.
+            bind_emails (List[str]): list of emails to bind to this account.
         Returns:
             A tuple of (user_id, access_token).
         Raises:
@@ -261,6 +263,21 @@ class RegistrationHandler(BaseHandler):
         if not self.hs.config.user_consent_at_registration:
             yield self._auto_join_rooms(user_id)
 
+        # Bind any specified emails to this account
+        current_time = self.hs.get_clock().time_msec()
+        for email in bind_emails:
+            # generate threepid dict
+            threepid_dict = {
+                "medium": "email",
+                "address": email,
+                "validated_at": current_time,
+            }
+
+            # Bind email to new account
+            yield self._register_email_threepid(
+                user_id, threepid_dict, None, False,
+            )
+
         defer.returnValue((user_id, token))
 
     @defer.inlineCallbacks