Add ability to perform password reset via email without trusting the identity server (#5377)

Sends password reset emails from the homeserver instead of proxying to the identity server. This is now the default behaviour for security reasons. If you wish to continue proxying password reset requests to the identity server you must now enable the email.trust_identity_server_for_password_resets option.

This PR is a culmination of 3 smaller PRs which have each been separately reviewed:

* #5308
* #5345
* #5368

2 files changed, 63 insertions, 14 deletions

diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index aa5d89a9ac..7f8ddc99c6 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -162,7 +162,7 @@ class AuthHandler(BaseHandler):
         defer.returnValue(params)
 
     @defer.inlineCallbacks
-    def check_auth(self, flows, clientdict, clientip):
+    def check_auth(self, flows, clientdict, clientip, password_servlet=False):
         """
         Takes a dictionary sent by the client in the login / registration
         protocol and handles the User-Interactive Auth flow.
@@ -186,6 +186,16 @@ class AuthHandler(BaseHandler):
 
             clientip (str): The IP address of the client.
 
+            password_servlet (bool): Whether the request originated from
+                PasswordRestServlet.
+                XXX: This is a temporary hack to distinguish between checking
+                for threepid validations locally (in the case of password
+                resets) and using the identity server (in the case of binding
+                a 3PID during registration). Once we start using the
+                homeserver for both tasks, this distinction will no longer be
+                necessary.
+
+
         Returns:
             defer.Deferred[dict, dict, str]: a deferred tuple of
                 (creds, params, session_id).
@@ -241,7 +251,9 @@ class AuthHandler(BaseHandler):
         if 'type' in authdict:
             login_type = authdict['type']
             try:
-                result = yield self._check_auth_dict(authdict, clientip)
+                result = yield self._check_auth_dict(
+                    authdict, clientip, password_servlet=password_servlet,
+                )
                 if result:
                     creds[login_type] = result
                     self._save_session(session)
@@ -351,7 +363,7 @@ class AuthHandler(BaseHandler):
         return sess.setdefault('serverdict', {}).get(key, default)
 
     @defer.inlineCallbacks
-    def _check_auth_dict(self, authdict, clientip):
+    def _check_auth_dict(self, authdict, clientip, password_servlet=False):
         """Attempt to validate the auth dict provided by a client
 
         Args:
@@ -369,7 +381,13 @@ class AuthHandler(BaseHandler):
         login_type = authdict['type']
         checker = self.checkers.get(login_type)
         if checker is not None:
-            res = yield checker(authdict, clientip)
+            # XXX: Temporary workaround for having Synapse handle password resets
+            # See AuthHandler.check_auth for further details
+            res = yield checker(
+                authdict,
+                clientip=clientip,
+                password_servlet=password_servlet,
+            )
             defer.returnValue(res)
 
         # build a v1-login-style dict out of the authdict and fall back to the
@@ -383,7 +401,7 @@ class AuthHandler(BaseHandler):
         defer.returnValue(canonical_id)
 
     @defer.inlineCallbacks
-    def _check_recaptcha(self, authdict, clientip):
+    def _check_recaptcha(self, authdict, clientip, **kwargs):
         try:
             user_response = authdict["response"]
         except KeyError:
@@ -429,20 +447,20 @@ class AuthHandler(BaseHandler):
                 defer.returnValue(True)
         raise LoginError(401, "", errcode=Codes.UNAUTHORIZED)
 
-    def _check_email_identity(self, authdict, _):
-        return self._check_threepid('email', authdict)
+    def _check_email_identity(self, authdict, **kwargs):
+        return self._check_threepid('email', authdict, **kwargs)
 
-    def _check_msisdn(self, authdict, _):
+    def _check_msisdn(self, authdict, **kwargs):
         return self._check_threepid('msisdn', authdict)
 
-    def _check_dummy_auth(self, authdict, _):
+    def _check_dummy_auth(self, authdict, **kwargs):
         return defer.succeed(True)
 
-    def _check_terms_auth(self, authdict, _):
+    def _check_terms_auth(self, authdict, **kwargs):
         return defer.succeed(True)
 
     @defer.inlineCallbacks
-    def _check_threepid(self, medium, authdict):
+    def _check_threepid(self, medium, authdict, password_servlet=False, **kwargs):
         if 'threepid_creds' not in authdict:
             raise LoginError(400, "Missing threepid_creds", Codes.MISSING_PARAM)
 
@@ -451,7 +469,29 @@ class AuthHandler(BaseHandler):
         identity_handler = self.hs.get_handlers().identity_handler
 
         logger.info("Getting validated threepid. threepidcreds: %r", (threepid_creds,))
-        threepid = yield identity_handler.threepid_from_creds(threepid_creds)
+        if (
+            not password_servlet
+            or self.hs.config.email_password_reset_behaviour == "remote"
+        ):
+            threepid = yield identity_handler.threepid_from_creds(threepid_creds)
+        elif self.hs.config.email_password_reset_behaviour == "local":
+            row = yield self.store.get_threepid_validation_session(
+                medium,
+                threepid_creds["client_secret"],
+                sid=threepid_creds["sid"],
+            )
+
+            threepid = {
+                "medium": row["medium"],
+                "address": row["address"],
+                "validated_at": row["validated_at"],
+            } if row else None
+
+            if row:
+                # Valid threepid returned, delete from the db
+                yield self.store.delete_threepid_session(threepid_creds["sid"])
+        else:
+            raise SynapseError(400, "Password resets are not enabled on this homeserver")
 
         if not threepid:
             raise LoginError(401, "", errcode=Codes.UNAUTHORIZED)
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py
index 22469486d7..04caf65793 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -247,7 +247,14 @@ class IdentityHandler(BaseHandler):
         defer.returnValue(changed)
 
     @defer.inlineCallbacks
-    def requestEmailToken(self, id_server, email, client_secret, send_attempt, **kwargs):
+    def requestEmailToken(
+        self,
+        id_server,
+        email,
+        client_secret,
+        send_attempt,
+        next_link=None,
+    ):
         if not self._should_trust_id_server(id_server):
             raise SynapseError(
                 400, "Untrusted ID server '%s'" % id_server,
@@ -259,7 +266,9 @@ class IdentityHandler(BaseHandler):
             'client_secret': client_secret,
             'send_attempt': send_attempt,
         }
-        params.update(kwargs)
+
+        if next_link:
+            params.update({'next_link': next_link})
 
         try:
             data = yield self.http_client.post_json_get_json(