Allow guests to register and call /events?room_id=

This follows the same flows-based flow as regular registration, but as
the only implemented flow has no requirements, it auto-succeeds. In the
future, other flows (e.g. captcha) may be required, so clients should
treat this like the regular registration flow choices.

27 files changed, 224 insertions, 149 deletions

diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 88445fe999..dfbbc5a1cd 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -49,6 +49,7 @@ class Auth(object):
         self.TOKEN_NOT_FOUND_HTTP_STATUS = 401
         self._KNOWN_CAVEAT_PREFIXES = set([
             "gen = ",
+            "guest = ",
             "type = ",
             "time < ",
             "user_id = ",
@@ -183,15 +184,11 @@ class Auth(object):
         defer.returnValue(member)
 
     @defer.inlineCallbacks
-    def check_user_was_in_room(self, room_id, user_id, current_state=None):
+    def check_user_was_in_room(self, room_id, user_id):
         """Check if the user was in the room at some point.
         Args:
             room_id(str): The room to check.
             user_id(str): The user to check.
-            current_state(dict): Optional map of the current state of the room.
-                If provided then that map is used to check whether they are a
-                member of the room. Otherwise the current membership is
-                loaded from the database.
         Raises:
             AuthError if the user was never in the room.
         Returns:
@@ -199,17 +196,11 @@ class Auth(object):
             room. This will be the join event if they are currently joined to
             the room. This will be the leave event if they have left the room.
         """
-        if current_state:
-            member = current_state.get(
-                (EventTypes.Member, user_id),
-                None
-            )
-        else:
-            member = yield self.state.get_current_state(
-                room_id=room_id,
-                event_type=EventTypes.Member,
-                state_key=user_id
-            )
+        member = yield self.state.get_current_state(
+            room_id=room_id,
+            event_type=EventTypes.Member,
+            state_key=user_id
+        )
         membership = member.membership if member else None
 
         if membership not in (Membership.JOIN, Membership.LEAVE):
@@ -497,7 +488,7 @@ class Auth(object):
             return default
 
     @defer.inlineCallbacks
-    def get_user_by_req(self, request):
+    def get_user_by_req(self, request, allow_guest=False):
         """ Get a registered user's ID.
 
         Args:
@@ -535,7 +526,7 @@ class Auth(object):
 
                 request.authenticated_entity = user_id
 
-                defer.returnValue((UserID.from_string(user_id), ""))
+                defer.returnValue((UserID.from_string(user_id), "", False))
                 return
             except KeyError:
                 pass  # normal users won't have the user_id query parameter set.
@@ -543,6 +534,7 @@ class Auth(object):
             user_info = yield self._get_user_by_access_token(access_token)
             user = user_info["user"]
             token_id = user_info["token_id"]
+            is_guest = user_info["is_guest"]
 
             ip_addr = self.hs.get_ip_from_request(request)
             user_agent = request.requestHeaders.getRawHeaders(
@@ -557,9 +549,14 @@ class Auth(object):
                     user_agent=user_agent
                 )
 
+            if is_guest and not allow_guest:
+                raise AuthError(
+                    403, "Guest access not allowed", errcode=Codes.GUEST_ACCESS_FORBIDDEN
+                )
+
             request.authenticated_entity = user.to_string()
 
-            defer.returnValue((user, token_id,))
+            defer.returnValue((user, token_id, is_guest,))
         except KeyError:
             raise AuthError(
                 self.TOKEN_NOT_FOUND_HTTP_STATUS, "Missing access token.",
@@ -592,31 +589,45 @@ class Auth(object):
             self._validate_macaroon(macaroon)
 
             user_prefix = "user_id = "
+            user = None
+            guest = False
             for caveat in macaroon.caveats:
                 if caveat.caveat_id.startswith(user_prefix):
                     user = UserID.from_string(caveat.caveat_id[len(user_prefix):])
-                    # This codepath exists so that we can actually return a
-                    # token ID, because we use token IDs in place of device
-                    # identifiers throughout the codebase.
-                    # TODO(daniel): Remove this fallback when device IDs are
-                    # properly implemented.
-                    ret = yield self._look_up_user_by_access_token(macaroon_str)
-                    if ret["user"] != user:
-                        logger.error(
-                            "Macaroon user (%s) != DB user (%s)",
-                            user,
-                            ret["user"]
-                        )
-                        raise AuthError(
-                            self.TOKEN_NOT_FOUND_HTTP_STATUS,
-                            "User mismatch in macaroon",
-                            errcode=Codes.UNKNOWN_TOKEN
-                        )
-                    defer.returnValue(ret)
-            raise AuthError(
-                self.TOKEN_NOT_FOUND_HTTP_STATUS, "No user caveat in macaroon",
-                errcode=Codes.UNKNOWN_TOKEN
-            )
+                elif caveat.caveat_id == "guest = true":
+                    guest = True
+
+            if user is None:
+                raise AuthError(
+                    self.TOKEN_NOT_FOUND_HTTP_STATUS, "No user caveat in macaroon",
+                    errcode=Codes.UNKNOWN_TOKEN
+                )
+
+            if guest:
+                ret = {
+                    "user": user,
+                    "is_guest": True,
+                    "token_id": None,
+                }
+            else:
+                # This codepath exists so that we can actually return a
+                # token ID, because we use token IDs in place of device
+                # identifiers throughout the codebase.
+                # TODO(daniel): Remove this fallback when device IDs are
+                # properly implemented.
+                ret = yield self._look_up_user_by_access_token(macaroon_str)
+                if ret["user"] != user:
+                    logger.error(
+                        "Macaroon user (%s) != DB user (%s)",
+                        user,
+                        ret["user"]
+                    )
+                    raise AuthError(
+                        self.TOKEN_NOT_FOUND_HTTP_STATUS,
+                        "User mismatch in macaroon",
+                        errcode=Codes.UNKNOWN_TOKEN
+                    )
+            defer.returnValue(ret)
         except (pymacaroons.exceptions.MacaroonException, TypeError, ValueError):
             raise AuthError(
                 self.TOKEN_NOT_FOUND_HTTP_STATUS, "Invalid macaroon passed.",
@@ -629,6 +640,7 @@ class Auth(object):
         v.satisfy_exact("type = access")
         v.satisfy_general(lambda c: c.startswith("user_id = "))
         v.satisfy_general(self._verify_expiry)
+        v.satisfy_exact("guest = true")
         v.verify(macaroon, self.hs.config.macaroon_secret_key)
 
         v = pymacaroons.Verifier()
@@ -666,6 +678,7 @@ class Auth(object):
         user_info = {
             "user": UserID.from_string(ret.get("name")),
             "token_id": ret.get("token_id", None),
+            "is_guest": False,
         }
         defer.returnValue(user_info)
 
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index b3fea27d0e..d4037b3d55 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -33,6 +33,7 @@ class Codes(object):
     NOT_FOUND = "M_NOT_FOUND"
     MISSING_TOKEN = "M_MISSING_TOKEN"
     UNKNOWN_TOKEN = "M_UNKNOWN_TOKEN"
+    GUEST_ACCESS_FORBIDDEN = "M_GUEST_ACCESS_FORBIDDEN"
     LIMIT_EXCEEDED = "M_LIMIT_EXCEEDED"
     CAPTCHA_NEEDED = "M_CAPTCHA_NEEDED"
     CAPTCHA_INVALID = "M_CAPTCHA_INVALID"
diff --git a/synapse/config/registration.py b/synapse/config/registration.py
index f5ef36a9f4..dca391f7af 100644
--- a/synapse/config/registration.py
+++ b/synapse/config/registration.py
@@ -34,6 +34,7 @@ class RegistrationConfig(Config):
         self.registration_shared_secret = config.get("registration_shared_secret")
         self.macaroon_secret_key = config.get("macaroon_secret_key")
         self.bcrypt_rounds = config.get("bcrypt_rounds", 12)
+        self.allow_guest_access = config.get("allow_guest_access", False)
 
     def default_config(self, **kwargs):
         registration_shared_secret = random_string_with_symbols(50)
@@ -54,6 +55,11 @@ class RegistrationConfig(Config):
         # Larger numbers increase the work factor needed to generate the hash.
         # The default number of rounds is 12.
         bcrypt_rounds: 12
+
+        # Allows users to register as guests without a password/email/etc, and
+        # participate in rooms hosted on this server which have been made
+        # accessible to anonymous users.
+        allow_guest_access: False
         """ % locals()
 
     def add_arguments(self, parser):
diff --git a/synapse/handlers/_base.py b/synapse/handlers/_base.py
index 6a26cb1879..6873a4575d 100644
--- a/synapse/handlers/_base.py
+++ b/synapse/handlers/_base.py
@@ -47,37 +47,23 @@ class BaseHandler(object):
         self.event_builder_factory = hs.get_event_builder_factory()
 
     @defer.inlineCallbacks
-    def _filter_events_for_client(self, user_id, events):
-        event_id_to_state = yield self.store.get_state_for_events(
-            frozenset(e.event_id for e in events),
-            types=(
-                (EventTypes.RoomHistoryVisibility, ""),
-                (EventTypes.Member, user_id),
-            )
-        )
+    def _filter_events_for_client(self, user_id, events, is_guest=False):
+        # Assumes that user has at some point joined the room if not is_guest.
 
-        def allowed(event, state):
-            if event.type == EventTypes.RoomHistoryVisibility:
+        def allowed(event, membership, visibility):
+            if visibility == "world_readable":
                 return True
 
-            membership_ev = state.get((EventTypes.Member, user_id), None)
-            if membership_ev:
-                membership = membership_ev.membership
-            else:
-                membership = Membership.LEAVE
+            if is_guest:
+                return False
 
             if membership == Membership.JOIN:
                 return True
 
-            history = state.get((EventTypes.RoomHistoryVisibility, ''), None)
-            if history:
-                visibility = history.content.get("history_visibility", "shared")
-            else:
-                visibility = "shared"
+            if event.type == EventTypes.RoomHistoryVisibility:
+                return not is_guest
 
-            if visibility == "public":
-                return True
-            elif visibility == "shared":
+            if visibility == "shared":
                 return True
             elif visibility == "joined":
                 return membership == Membership.JOIN
@@ -86,11 +72,44 @@ class BaseHandler(object):
 
             return True
 
-        defer.returnValue([
-            event
-            for event in events
-            if allowed(event, event_id_to_state[event.event_id])
-        ])
+        event_id_to_state = yield self.store.get_state_for_events(
+            frozenset(e.event_id for e in events),
+            types=(
+                (EventTypes.RoomHistoryVisibility, ""),
+                (EventTypes.Member, user_id),
+            )
+        )
+
+        events_to_return = []
+        for event in events:
+            state = event_id_to_state[event.event_id]
+
+            membership_event = state.get((EventTypes.Member, user_id), None)
+            if membership_event:
+                membership = membership_event.membership
+            else:
+                membership = None
+
+            visibility_event = state.get((EventTypes.RoomHistoryVisibility, ""), None)
+            if visibility_event:
+                visibility = visibility_event.content.get("history_visibility", "shared")
+            else:
+                visibility = "shared"
+
+            should_include = allowed(event, membership, visibility)
+            if should_include:
+                events_to_return.append(event)
+
+        if is_guest and len(events_to_return) < len(events):
+            # This indicates that some events in the requested range were not
+            # visible to guest users. To be safe, we reject the entire request,
+            # so that we don't have to worry about interpreting visibility
+            # boundaries.
+            raise AuthError(403, "User %s does not have permission" % (
+                user_id
+            ))
+
+        defer.returnValue(events_to_return)
 
     def ratelimit(self, user_id):
         time_now = self.clock.time()
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 055d395b20..1b11dbdffd 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -372,12 +372,15 @@ class AuthHandler(BaseHandler):
         yield self.store.add_refresh_token_to_user(user_id, refresh_token)
         defer.returnValue(refresh_token)
 
-    def generate_access_token(self, user_id):
+    def generate_access_token(self, user_id, extra_caveats=None):
+        extra_caveats = extra_caveats or []
         macaroon = self._generate_base_macaroon(user_id)
         macaroon.add_first_party_caveat("type = access")
         now = self.hs.get_clock().time_msec()
         expiry = now + (60 * 60 * 1000)
         macaroon.add_first_party_caveat("time < %d" % (expiry,))
+        for caveat in extra_caveats:
+            macaroon.add_first_party_caveat(caveat)
         return macaroon.serialize()
 
     def generate_refresh_token(self, user_id):
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 0f947993d1..687e1527f7 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -71,20 +71,20 @@ class MessageHandler(BaseHandler):
 
     @defer.inlineCallbacks
     def get_messages(self, user_id=None, room_id=None, pagin_config=None,
-                     as_client_event=True):
+                     as_client_event=True, is_guest=False):
         """Get messages in a room.
 
         Args:
             user_id (str): The user requesting messages.
             room_id (str): The room they want messages from.
             pagin_config (synapse.api.streams.PaginationConfig): The pagination
-            config rules to apply, if any.
+                config rules to apply, if any.
             as_client_event (bool): True to get events in client-server format.
+            is_guest (bool): Whether the requesting user is a guest (as opposed
+                to a fully registered user).
         Returns:
             dict: Pagination API results
         """
-        member_event = yield self.auth.check_user_was_in_room(room_id, user_id)
-
         data_source = self.hs.get_event_sources().sources["room"]
 
         if pagin_config.from_token:
@@ -107,23 +107,27 @@ class MessageHandler(BaseHandler):
 
         source_config = pagin_config.get_source_config("room")
 
-        if member_event.membership == Membership.LEAVE:
-            # If they have left the room then clamp the token to be before
-            # they left the room
-            leave_token = yield self.store.get_topological_token_for_event(
-                member_event.event_id
-            )
-            leave_token = RoomStreamToken.parse(leave_token)
-            if leave_token.topological < room_token.topological:
-                source_config.from_key = str(leave_token)
-
-            if source_config.direction == "f":
-                if source_config.to_key is None:
-                    source_config.to_key = str(leave_token)
-                else:
-                    to_token = RoomStreamToken.parse(source_config.to_key)
-                    if leave_token.topological < to_token.topological:
+        if not is_guest:
+            member_event = yield self.auth.check_user_was_in_room(room_id, user_id)
+            if member_event.membership == Membership.LEAVE:
+                # If they have left the room then clamp the token to be before
+                # they left the room.
+                # If they're a guest, we'll just 403 them if they're asking for
+                # events they can't see.
+                leave_token = yield self.store.get_topological_token_for_event(
+                    member_event.event_id
+                )
+                leave_token = RoomStreamToken.parse(leave_token)
+                if leave_token.topological < room_token.topological:
+                    source_config.from_key = str(leave_token)
+
+                if source_config.direction == "f":
+                    if source_config.to_key is None:
                         source_config.to_key = str(leave_token)
+                    else:
+                        to_token = RoomStreamToken.parse(source_config.to_key)
+                        if leave_token.topological < to_token.topological:
+                            source_config.to_key = str(leave_token)
 
         yield self.hs.get_handlers().federation_handler.maybe_backfill(
             room_id, room_token.topological
@@ -146,7 +150,7 @@ class MessageHandler(BaseHandler):
                 "end": next_token.to_string(),
             })
 
-        events = yield self._filter_events_for_client(user_id, events)
+        events = yield self._filter_events_for_client(user_id, events, is_guest=is_guest)
 
         time_now = self.clock.time_msec()
 
diff --git a/synapse/handlers/register.py b/synapse/handlers/register.py
index ef4081e3fe..493a087031 100644
--- a/synapse/handlers/register.py
+++ b/synapse/handlers/register.py
@@ -64,7 +64,7 @@ class RegistrationHandler(BaseHandler):
             )
 
     @defer.inlineCallbacks
-    def register(self, localpart=None, password=None):
+    def register(self, localpart=None, password=None, generate_token=True):
         """Registers a new client on the server.
 
         Args:
@@ -89,7 +89,9 @@ class RegistrationHandler(BaseHandler):
             user = UserID(localpart, self.hs.hostname)
             user_id = user.to_string()
 
-            token = self.auth_handler().generate_access_token(user_id)
+            token = None
+            if generate_token:
+                token = self.auth_handler().generate_access_token(user_id)
             yield self.store.register(
                 user_id=user_id,
                 token=token,
@@ -102,14 +104,14 @@ class RegistrationHandler(BaseHandler):
             attempts = 0
             user_id = None
             token = None
-            while not user_id and not token:
+            while not user_id:
                 try:
                     localpart = self._generate_user_id()
                     user = UserID(localpart, self.hs.hostname)
                     user_id = user.to_string()
                     yield self.check_user_id_is_valid(user_id)
-
-                    token = self.auth_handler().generate_access_token(user_id)
+                    if generate_token:
+                        token = self.auth_handler().generate_access_token(user_id)
                     yield self.store.register(
                         user_id=user_id,
                         token=token,
diff --git a/synapse/rest/client/v1/admin.py b/synapse/rest/client/v1/admin.py
index 504b63eab4..bdde43864c 100644
--- a/synapse/rest/client/v1/admin.py
+++ b/synapse/rest/client/v1/admin.py
@@ -31,7 +31,7 @@ class WhoisRestServlet(ClientV1RestServlet):
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
         target_user = UserID.from_string(user_id)
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         is_admin = yield self.auth.is_server_admin(auth_user)
 
         if not is_admin and target_user != auth_user:
diff --git a/synapse/rest/client/v1/directory.py b/synapse/rest/client/v1/directory.py
index 4dcda57c1b..240eedac75 100644
--- a/synapse/rest/client/v1/directory.py
+++ b/synapse/rest/client/v1/directory.py
@@ -69,7 +69,7 @@ class ClientDirectoryServer(ClientV1RestServlet):
 
         try:
             # try to auth as a user
-            user, _ = yield self.auth.get_user_by_req(request)
+            user, _, _ = yield self.auth.get_user_by_req(request)
             try:
                 user_id = user.to_string()
                 yield dir_handler.create_association(
@@ -116,7 +116,7 @@ class ClientDirectoryServer(ClientV1RestServlet):
             # fallback to default user behaviour if they aren't an AS
             pass
 
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
 
         is_admin = yield self.auth.is_server_admin(user)
         if not is_admin:
diff --git a/synapse/rest/client/v1/events.py b/synapse/rest/client/v1/events.py
index 582148b659..4073b0d2d1 100644
--- a/synapse/rest/client/v1/events.py
+++ b/synapse/rest/client/v1/events.py
@@ -34,7 +34,7 @@ class EventStreamRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         try:
             handler = self.handlers.event_stream_handler
             pagin_config = PaginationConfig.from_request(request)
@@ -71,7 +71,7 @@ class EventRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, event_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         handler = self.handlers.event_handler
         event = yield handler.get_event(auth_user, event_id)
 
diff --git a/synapse/rest/client/v1/initial_sync.py b/synapse/rest/client/v1/initial_sync.py
index 52c7943400..856a70f297 100644
--- a/synapse/rest/client/v1/initial_sync.py
+++ b/synapse/rest/client/v1/initial_sync.py
@@ -25,7 +25,7 @@ class InitialSyncRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
         as_client_event = "raw" not in request.args
         pagination_config = PaginationConfig.from_request(request)
         handler = self.handlers.message_handler
diff --git a/synapse/rest/client/v1/presence.py b/synapse/rest/client/v1/presence.py
index a770efd841..6fe5d19a22 100644
--- a/synapse/rest/client/v1/presence.py
+++ b/synapse/rest/client/v1/presence.py
@@ -32,7 +32,7 @@ class PresenceStatusRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user = UserID.from_string(user_id)
 
         state = yield self.handlers.presence_handler.get_state(
@@ -42,7 +42,7 @@ class PresenceStatusRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user = UserID.from_string(user_id)
 
         state = {}
@@ -77,7 +77,7 @@ class PresenceListRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user = UserID.from_string(user_id)
 
         if not self.hs.is_mine(user):
@@ -97,7 +97,7 @@ class PresenceListRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user = UserID.from_string(user_id)
 
         if not self.hs.is_mine(user):
diff --git a/synapse/rest/client/v1/profile.py b/synapse/rest/client/v1/profile.py
index fdde88a60d..6b379e4e5f 100644
--- a/synapse/rest/client/v1/profile.py
+++ b/synapse/rest/client/v1/profile.py
@@ -37,7 +37,7 @@ class ProfileDisplaynameRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user = UserID.from_string(user_id)
 
         try:
@@ -70,7 +70,7 @@ class ProfileAvatarURLRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user = UserID.from_string(user_id)
 
         try:
diff --git a/synapse/rest/client/v1/push_rule.py b/synapse/rest/client/v1/push_rule.py
index bd759a2589..b0870db1ac 100644
--- a/synapse/rest/client/v1/push_rule.py
+++ b/synapse/rest/client/v1/push_rule.py
@@ -43,7 +43,7 @@ class PushRuleRestServlet(ClientV1RestServlet):
         except InvalidRuleException as e:
             raise SynapseError(400, e.message)
 
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
 
         if '/' in spec['rule_id'] or '\\' in spec['rule_id']:
             raise SynapseError(400, "rule_id may not contain slashes")
@@ -92,7 +92,7 @@ class PushRuleRestServlet(ClientV1RestServlet):
     def on_DELETE(self, request):
         spec = _rule_spec_from_path(request.postpath)
 
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
 
         namespaced_rule_id = _namespaced_rule_id_from_spec(spec)
 
@@ -109,7 +109,7 @@ class PushRuleRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
 
         # we build up the full structure and then decide which bits of it
         # to send which means doing unnecessary work sometimes but is
diff --git a/synapse/rest/client/v1/pusher.py b/synapse/rest/client/v1/pusher.py
index 3aabc93b8b..a110c0a4f0 100644
--- a/synapse/rest/client/v1/pusher.py
+++ b/synapse/rest/client/v1/pusher.py
@@ -27,7 +27,7 @@ class PusherRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
 
         content = _parse_json(request)
 
diff --git a/synapse/rest/client/v1/room.py b/synapse/rest/client/v1/room.py
index 2dcaee86cd..0876e593c5 100644
--- a/synapse/rest/client/v1/room.py
+++ b/synapse/rest/client/v1/room.py
@@ -62,7 +62,7 @@ class RoomCreateRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         room_config = self.get_room_config(request)
         info = yield self.make_room(room_config, auth_user, None)
@@ -125,7 +125,7 @@ class RoomStateEventRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, room_id, event_type, state_key):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
 
         msg_handler = self.handlers.message_handler
         data = yield msg_handler.get_room_data(
@@ -143,7 +143,7 @@ class RoomStateEventRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, room_id, event_type, state_key, txn_id=None):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
 
         content = _parse_json(request)
 
@@ -175,7 +175,7 @@ class RoomSendEventRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, room_id, event_type, txn_id=None):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
         content = _parse_json(request)
 
         msg_handler = self.handlers.message_handler
@@ -220,7 +220,7 @@ class JoinRoomAliasServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, room_identifier, txn_id=None):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
 
         # the identifier could be a room alias or a room id. Try one then the
         # other if it fails to parse, without swallowing other valid
@@ -289,7 +289,7 @@ class RoomMemberListRestServlet(ClientV1RestServlet):
     @defer.inlineCallbacks
     def on_GET(self, request, room_id):
         # TODO support Pagination stream API (limit/tokens)
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
         handler = self.handlers.message_handler
         events = yield handler.get_state_events(
             room_id=room_id,
@@ -325,7 +325,7 @@ class RoomMessageListRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, room_id):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, is_guest = yield self.auth.get_user_by_req(request, allow_guest=True)
         pagination_config = PaginationConfig.from_request(
             request, default_limit=10,
         )
@@ -334,6 +334,7 @@ class RoomMessageListRestServlet(ClientV1RestServlet):
         msgs = yield handler.get_messages(
             room_id=room_id,
             user_id=user.to_string(),
+            is_guest=is_guest,
             pagin_config=pagination_config,
             as_client_event=as_client_event
         )
@@ -347,7 +348,7 @@ class RoomStateRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, room_id):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
         handler = self.handlers.message_handler
         # Get all the current state for this room
         events = yield handler.get_state_events(
@@ -363,7 +364,7 @@ class RoomInitialSyncRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, room_id):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
         pagination_config = PaginationConfig.from_request(request)
         content = yield self.handlers.message_handler.room_initial_sync(
             room_id=room_id,
@@ -443,7 +444,7 @@ class RoomMembershipRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, room_id, membership_action, txn_id=None):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
 
         content = _parse_json(request)
 
@@ -524,7 +525,7 @@ class RoomRedactEventRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, room_id, event_id, txn_id=None):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
         content = _parse_json(request)
 
         msg_handler = self.handlers.message_handler
@@ -564,7 +565,7 @@ class RoomTypingRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, room_id, user_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         room_id = urllib.unquote(room_id)
         target_user = UserID.from_string(urllib.unquote(user_id))
@@ -597,7 +598,7 @@ class SearchRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         content = _parse_json(request)
 
diff --git a/synapse/rest/client/v1/voip.py b/synapse/rest/client/v1/voip.py
index 0a863e1c61..eb7c57cade 100644
--- a/synapse/rest/client/v1/voip.py
+++ b/synapse/rest/client/v1/voip.py
@@ -28,7 +28,7 @@ class VoipRestServlet(ClientV1RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         turnUris = self.hs.config.turn_uris
         turnSecret = self.hs.config.turn_shared_secret
diff --git a/synapse/rest/client/v2_alpha/account.py b/synapse/rest/client/v2_alpha/account.py
index 4692ba413c..1970ad3458 100644
--- a/synapse/rest/client/v2_alpha/account.py
+++ b/synapse/rest/client/v2_alpha/account.py
@@ -55,7 +55,7 @@ class PasswordRestServlet(RestServlet):
 
         if LoginType.PASSWORD in result:
             # if using password, they should also be logged in
-            auth_user, _ = yield self.auth.get_user_by_req(request)
+            auth_user, _, _ = yield self.auth.get_user_by_req(request)
             if auth_user.to_string() != result[LoginType.PASSWORD]:
                 raise LoginError(400, "", Codes.UNKNOWN)
             user_id = auth_user.to_string()
@@ -102,7 +102,7 @@ class ThreepidRestServlet(RestServlet):
     def on_GET(self, request):
         yield run_on_reactor()
 
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         threepids = yield self.hs.get_datastore().user_get_threepids(
             auth_user.to_string()
@@ -120,7 +120,7 @@ class ThreepidRestServlet(RestServlet):
             raise SynapseError(400, "Missing param", Codes.MISSING_PARAM)
         threePidCreds = body['threePidCreds']
 
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         threepid = yield self.identity_handler.threepid_from_creds(threePidCreds)
 
diff --git a/synapse/rest/client/v2_alpha/filter.py b/synapse/rest/client/v2_alpha/filter.py
index f8f91b63f5..97956a4b91 100644
--- a/synapse/rest/client/v2_alpha/filter.py
+++ b/synapse/rest/client/v2_alpha/filter.py
@@ -40,7 +40,7 @@ class GetFilterRestServlet(RestServlet):
     @defer.inlineCallbacks
     def on_GET(self, request, user_id, filter_id):
         target_user = UserID.from_string(user_id)
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         if target_user != auth_user:
             raise AuthError(403, "Cannot get filters for other users")
@@ -76,7 +76,7 @@ class CreateFilterRestServlet(RestServlet):
     @defer.inlineCallbacks
     def on_POST(self, request, user_id):
         target_user = UserID.from_string(user_id)
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         if target_user != auth_user:
             raise AuthError(403, "Cannot create filters for other users")
diff --git a/synapse/rest/client/v2_alpha/keys.py b/synapse/rest/client/v2_alpha/keys.py
index a1f4423101..820d33336f 100644
--- a/synapse/rest/client/v2_alpha/keys.py
+++ b/synapse/rest/client/v2_alpha/keys.py
@@ -64,7 +64,7 @@ class KeyUploadServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, device_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user_id = auth_user.to_string()
         # TODO: Check that the device_id matches that in the authentication
         # or derive the device_id from the authentication instead.
@@ -109,7 +109,7 @@ class KeyUploadServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, device_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         user_id = auth_user.to_string()
 
         result = yield self.store.count_e2e_one_time_keys(user_id, device_id)
@@ -181,7 +181,7 @@ class KeyQueryServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id, device_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         auth_user_id = auth_user.to_string()
         user_id = user_id if user_id else auth_user_id
         device_ids = [device_id] if device_id else []
diff --git a/synapse/rest/client/v2_alpha/receipts.py b/synapse/rest/client/v2_alpha/receipts.py
index b107b7ce17..788acd4adb 100644
--- a/synapse/rest/client/v2_alpha/receipts.py
+++ b/synapse/rest/client/v2_alpha/receipts.py
@@ -40,7 +40,7 @@ class ReceiptRestServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_POST(self, request, room_id, receipt_type, event_id):
-        user, _ = yield self.auth.get_user_by_req(request)
+        user, _, _ = yield self.auth.get_user_by_req(request)
 
         if receipt_type != "m.read":
             raise SynapseError(400, "Receipt type must be 'm.read'")
diff --git a/synapse/rest/client/v2_alpha/register.py b/synapse/rest/client/v2_alpha/register.py
index 1ba2f29711..f899376311 100644
--- a/synapse/rest/client/v2_alpha/register.py
+++ b/synapse/rest/client/v2_alpha/register.py
@@ -16,7 +16,7 @@
 from twisted.internet import defer
 
 from synapse.api.constants import LoginType
-from synapse.api.errors import SynapseError, Codes
+from synapse.api.errors import SynapseError, Codes, UnrecognizedRequestError
 from synapse.http.servlet import RestServlet
 
 from ._base import client_v2_pattern, parse_json_dict_from_request
@@ -55,6 +55,19 @@ class RegisterRestServlet(RestServlet):
     def on_POST(self, request):
         yield run_on_reactor()
 
+        kind = "user"
+        if "kind" in request.args:
+            kind = request.args["kind"][0]
+
+        if kind == "guest":
+            ret = yield self._do_guest_registration()
+            defer.returnValue(ret)
+            return
+        elif kind != "user":
+            raise UnrecognizedRequestError(
+                "Do not understand membership kind: %s" % (kind,)
+            )
+
         if '/register/email/requestToken' in request.path:
             ret = yield self.onEmailTokenRequest(request)
             defer.returnValue(ret)
@@ -236,6 +249,18 @@ class RegisterRestServlet(RestServlet):
         ret = yield self.identity_handler.requestEmailToken(**body)
         defer.returnValue((200, ret))
 
+    @defer.inlineCallbacks
+    def _do_guest_registration(self):
+        if not self.hs.config.allow_guest_access:
+            defer.returnValue((403, "Guest access is disabled"))
+        user_id, _ = yield self.registration_handler.register(generate_token=False)
+        access_token = self.auth_handler.generate_access_token(user_id, ["guest = true"])
+        defer.returnValue((200, {
+            "user_id": user_id,
+            "access_token": access_token,
+            "home_server": self.hs.hostname,
+        }))
+
 
 def register_servlets(hs, http_server):
     RegisterRestServlet(hs).register(http_server)
diff --git a/synapse/rest/client/v2_alpha/sync.py b/synapse/rest/client/v2_alpha/sync.py
index 32a1087c91..d24507effa 100644
--- a/synapse/rest/client/v2_alpha/sync.py
+++ b/synapse/rest/client/v2_alpha/sync.py
@@ -81,7 +81,7 @@ class SyncRestServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request):
-        user, token_id = yield self.auth.get_user_by_req(request)
+        user, token_id, _ = yield self.auth.get_user_by_req(request)
 
         timeout = parse_integer(request, "timeout", default=0)
         since = parse_string(request, "since")
diff --git a/synapse/rest/client/v2_alpha/tags.py b/synapse/rest/client/v2_alpha/tags.py
index dcfe6bd20e..35482ae6a6 100644
--- a/synapse/rest/client/v2_alpha/tags.py
+++ b/synapse/rest/client/v2_alpha/tags.py
@@ -42,7 +42,7 @@ class TagListServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_GET(self, request, user_id, room_id):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         if user_id != auth_user.to_string():
             raise AuthError(403, "Cannot get tags for other users.")
 
@@ -68,7 +68,7 @@ class TagServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_PUT(self, request, user_id, room_id, tag):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         if user_id != auth_user.to_string():
             raise AuthError(403, "Cannot add tags for other users.")
 
@@ -88,7 +88,7 @@ class TagServlet(RestServlet):
 
     @defer.inlineCallbacks
     def on_DELETE(self, request, user_id, room_id, tag):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         if user_id != auth_user.to_string():
             raise AuthError(403, "Cannot add tags for other users.")
 
diff --git a/synapse/rest/media/v0/content_repository.py b/synapse/rest/media/v0/content_repository.py
index c28dc86cd7..e4fa8c4647 100644
--- a/synapse/rest/media/v0/content_repository.py
+++ b/synapse/rest/media/v0/content_repository.py
@@ -66,7 +66,7 @@ class ContentRepoResource(resource.Resource):
     @defer.inlineCallbacks
     def map_request_to_name(self, request):
         # auth the user
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
 
         # namespace all file uploads on the user
         prefix = base64.urlsafe_b64encode(
diff --git a/synapse/rest/media/v1/upload_resource.py b/synapse/rest/media/v1/upload_resource.py
index 6abaf56b25..7d61596082 100644
--- a/synapse/rest/media/v1/upload_resource.py
+++ b/synapse/rest/media/v1/upload_resource.py
@@ -70,7 +70,7 @@ class UploadResource(BaseMediaResource):
     @request_handler
     @defer.inlineCallbacks
     def _async_render_POST(self, request):
-        auth_user, _ = yield self.auth.get_user_by_req(request)
+        auth_user, _, _ = yield self.auth.get_user_by_req(request)
         # TODO: The checks here are a bit late. The content will have
         # already been uploaded to a tmp file at this point
         content_length = request.getHeader("Content-Length")
diff --git a/synapse/storage/registration.py b/synapse/storage/registration.py
index b454dd5b3a..2e5eddd259 100644
--- a/synapse/storage/registration.py
+++ b/synapse/storage/registration.py
@@ -102,13 +102,14 @@ class RegistrationStore(SQLBaseStore):
                 400, "User ID already taken.", errcode=Codes.USER_IN_USE
             )
 
-        # it's possible for this to get a conflict, but only for a single user
-        # since tokens are namespaced based on their user ID
-        txn.execute(
-            "INSERT INTO access_tokens(id, user_id, token)"
-            " VALUES (?,?,?)",
-            (next_id, user_id, token,)
-        )
+        if token:
+            # it's possible for this to get a conflict, but only for a single user
+            # since tokens are namespaced based on their user ID
+            txn.execute(
+                "INSERT INTO access_tokens(id, user_id, token)"
+                " VALUES (?,?,?)",
+                (next_id, user_id, token,)
+            )
 
     def get_user_by_id(self, user_id):
         return self._simple_select_one(