Merge pull request #1810 from matrix-org/erikj/state_auth_splitout_split

Split out static auth methods from Auth object

2 files changed, 649 insertions, 571 deletions

diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index f93e45a744..280d4c4452 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -16,18 +16,14 @@
 import logging
 
 import pymacaroons
-from canonicaljson import encode_canonical_json
-from signedjson.key import decode_verify_key_bytes
-from signedjson.sign import verify_signed_json, SignatureVerifyException
 from twisted.internet import defer
-from unpaddedbase64 import decode_base64
 
 import synapse.types
+from synapse import event_auth
 from synapse.api.constants import EventTypes, Membership, JoinRules
-from synapse.api.errors import AuthError, Codes, SynapseError, EventSizeError
-from synapse.types import UserID, get_domain_from_id
+from synapse.api.errors import AuthError, Codes
+from synapse.types import UserID
 from synapse.util.logcontext import preserve_context_over_fn
-from synapse.util.logutils import log_function
 from synapse.util.metrics import Measure
 
 logger = logging.getLogger(__name__)
@@ -78,147 +74,7 @@ class Auth(object):
             True if the auth checks pass.
         """
         with Measure(self.clock, "auth.check"):
-            self.check_size_limits(event)
-
-            if not hasattr(event, "room_id"):
-                raise AuthError(500, "Event has no room_id: %s" % event)
-
-            if do_sig_check:
-                sender_domain = get_domain_from_id(event.sender)
-                event_id_domain = get_domain_from_id(event.event_id)
-
-                is_invite_via_3pid = (
-                    event.type == EventTypes.Member
-                    and event.membership == Membership.INVITE
-                    and "third_party_invite" in event.content
-                )
-
-                # Check the sender's domain has signed the event
-                if not event.signatures.get(sender_domain):
-                    # We allow invites via 3pid to have a sender from a different
-                    # HS, as the sender must match the sender of the original
-                    # 3pid invite. This is checked further down with the
-                    # other dedicated membership checks.
-                    if not is_invite_via_3pid:
-                        raise AuthError(403, "Event not signed by sender's server")
-
-                # Check the event_id's domain has signed the event
-                if not event.signatures.get(event_id_domain):
-                    raise AuthError(403, "Event not signed by sending server")
-
-            if auth_events is None:
-                # Oh, we don't know what the state of the room was, so we
-                # are trusting that this is allowed (at least for now)
-                logger.warn("Trusting event: %s", event.event_id)
-                return True
-
-            if event.type == EventTypes.Create:
-                room_id_domain = get_domain_from_id(event.room_id)
-                if room_id_domain != sender_domain:
-                    raise AuthError(
-                        403,
-                        "Creation event's room_id domain does not match sender's"
-                    )
-                # FIXME
-                return True
-
-            creation_event = auth_events.get((EventTypes.Create, ""), None)
-
-            if not creation_event:
-                raise SynapseError(
-                    403,
-                    "Room %r does not exist" % (event.room_id,)
-                )
-
-            creating_domain = get_domain_from_id(event.room_id)
-            originating_domain = get_domain_from_id(event.sender)
-            if creating_domain != originating_domain:
-                if not self.can_federate(event, auth_events):
-                    raise AuthError(
-                        403,
-                        "This room has been marked as unfederatable."
-                    )
-
-            # FIXME: Temp hack
-            if event.type == EventTypes.Aliases:
-                if not event.is_state():
-                    raise AuthError(
-                        403,
-                        "Alias event must be a state event",
-                    )
-                if not event.state_key:
-                    raise AuthError(
-                        403,
-                        "Alias event must have non-empty state_key"
-                    )
-                sender_domain = get_domain_from_id(event.sender)
-                if event.state_key != sender_domain:
-                    raise AuthError(
-                        403,
-                        "Alias event's state_key does not match sender's domain"
-                    )
-                return True
-
-            logger.debug(
-                "Auth events: %s",
-                [a.event_id for a in auth_events.values()]
-            )
-
-            if event.type == EventTypes.Member:
-                allowed = self.is_membership_change_allowed(
-                    event, auth_events
-                )
-                if allowed:
-                    logger.debug("Allowing! %s", event)
-                else:
-                    logger.debug("Denying! %s", event)
-                return allowed
-
-            self.check_event_sender_in_room(event, auth_events)
-
-            # Special case to allow m.room.third_party_invite events wherever
-            # a user is allowed to issue invites.  Fixes
-            # https://github.com/vector-im/vector-web/issues/1208 hopefully
-            if event.type == EventTypes.ThirdPartyInvite:
-                user_level = self._get_user_power_level(event.user_id, auth_events)
-                invite_level = self._get_named_level(auth_events, "invite", 0)
-
-                if user_level < invite_level:
-                    raise AuthError(
-                        403, (
-                            "You cannot issue a third party invite for %s." %
-                            (event.content.display_name,)
-                        )
-                    )
-                else:
-                    return True
-
-            self._can_send_event(event, auth_events)
-
-            if event.type == EventTypes.PowerLevels:
-                self._check_power_levels(event, auth_events)
-
-            if event.type == EventTypes.Redaction:
-                self.check_redaction(event, auth_events)
-
-            logger.debug("Allowing! %s", event)
-
-    def check_size_limits(self, event):
-        def too_big(field):
-            raise EventSizeError("%s too large" % (field,))
-
-        if len(event.user_id) > 255:
-            too_big("user_id")
-        if len(event.room_id) > 255:
-            too_big("room_id")
-        if event.is_state() and len(event.state_key) > 255:
-            too_big("state_key")
-        if len(event.type) > 255:
-            too_big("type")
-        if len(event.event_id) > 255:
-            too_big("event_id")
-        if len(encode_canonical_json(event.get_pdu_json())) > 65536:
-            too_big("event")
+            event_auth.check(event, auth_events, do_sig_check=do_sig_check)
 
     @defer.inlineCallbacks
     def check_joined_room(self, room_id, user_id, current_state=None):
@@ -300,16 +156,6 @@ class Auth(object):
             )
             defer.returnValue(ret)
 
-    def check_event_sender_in_room(self, event, auth_events):
-        key = (EventTypes.Member, event.user_id, )
-        member_event = auth_events.get(key)
-
-        return self._check_joined_room(
-            member_event,
-            event.user_id,
-            event.room_id
-        )
-
     def _check_joined_room(self, member, user_id, room_id):
         if not member or member.membership != Membership.JOIN:
             raise AuthError(403, "User %s not in room %s (%s)" % (
@@ -321,267 +167,8 @@ class Auth(object):
 
         return creation_event.content.get("m.federate", True) is True
 
-    @log_function
-    def is_membership_change_allowed(self, event, auth_events):
-        membership = event.content["membership"]
-
-        # Check if this is the room creator joining:
-        if len(event.prev_events) == 1 and Membership.JOIN == membership:
-            # Get room creation event:
-            key = (EventTypes.Create, "", )
-            create = auth_events.get(key)
-            if create and event.prev_events[0][0] == create.event_id:
-                if create.content["creator"] == event.state_key:
-                    return True
-
-        target_user_id = event.state_key
-
-        creating_domain = get_domain_from_id(event.room_id)
-        target_domain = get_domain_from_id(target_user_id)
-        if creating_domain != target_domain:
-            if not self.can_federate(event, auth_events):
-                raise AuthError(
-                    403,
-                    "This room has been marked as unfederatable."
-                )
-
-        # get info about the caller
-        key = (EventTypes.Member, event.user_id, )
-        caller = auth_events.get(key)
-
-        caller_in_room = caller and caller.membership == Membership.JOIN
-        caller_invited = caller and caller.membership == Membership.INVITE
-
-        # get info about the target
-        key = (EventTypes.Member, target_user_id, )
-        target = auth_events.get(key)
-
-        target_in_room = target and target.membership == Membership.JOIN
-        target_banned = target and target.membership == Membership.BAN
-
-        key = (EventTypes.JoinRules, "", )
-        join_rule_event = auth_events.get(key)
-        if join_rule_event:
-            join_rule = join_rule_event.content.get(
-                "join_rule", JoinRules.INVITE
-            )
-        else:
-            join_rule = JoinRules.INVITE
-
-        user_level = self._get_user_power_level(event.user_id, auth_events)
-        target_level = self._get_user_power_level(
-            target_user_id, auth_events
-        )
-
-        # FIXME (erikj): What should we do here as the default?
-        ban_level = self._get_named_level(auth_events, "ban", 50)
-
-        logger.debug(
-            "is_membership_change_allowed: %s",
-            {
-                "caller_in_room": caller_in_room,
-                "caller_invited": caller_invited,
-                "target_banned": target_banned,
-                "target_in_room": target_in_room,
-                "membership": membership,
-                "join_rule": join_rule,
-                "target_user_id": target_user_id,
-                "event.user_id": event.user_id,
-            }
-        )
-
-        if Membership.INVITE == membership and "third_party_invite" in event.content:
-            if not self._verify_third_party_invite(event, auth_events):
-                raise AuthError(403, "You are not invited to this room.")
-            if target_banned:
-                raise AuthError(
-                    403, "%s is banned from the room" % (target_user_id,)
-                )
-            return True
-
-        if Membership.JOIN != membership:
-            if (caller_invited
-                    and Membership.LEAVE == membership
-                    and target_user_id == event.user_id):
-                return True
-
-            if not caller_in_room:  # caller isn't joined
-                raise AuthError(
-                    403,
-                    "%s not in room %s." % (event.user_id, event.room_id,)
-                )
-
-        if Membership.INVITE == membership:
-            # TODO (erikj): We should probably handle this more intelligently
-            # PRIVATE join rules.
-
-            # Invites are valid iff caller is in the room and target isn't.
-            if target_banned:
-                raise AuthError(
-                    403, "%s is banned from the room" % (target_user_id,)
-                )
-            elif target_in_room:  # the target is already in the room.
-                raise AuthError(403, "%s is already in the room." %
-                                     target_user_id)
-            else:
-                invite_level = self._get_named_level(auth_events, "invite", 0)
-
-                if user_level < invite_level:
-                    raise AuthError(
-                        403, "You cannot invite user %s." % target_user_id
-                    )
-        elif Membership.JOIN == membership:
-            # Joins are valid iff caller == target and they were:
-            # invited: They are accepting the invitation
-            # joined: It's a NOOP
-            if event.user_id != target_user_id:
-                raise AuthError(403, "Cannot force another user to join.")
-            elif target_banned:
-                raise AuthError(403, "You are banned from this room")
-            elif join_rule == JoinRules.PUBLIC:
-                pass
-            elif join_rule == JoinRules.INVITE:
-                if not caller_in_room and not caller_invited:
-                    raise AuthError(403, "You are not invited to this room.")
-            else:
-                # TODO (erikj): may_join list
-                # TODO (erikj): private rooms
-                raise AuthError(403, "You are not allowed to join this room")
-        elif Membership.LEAVE == membership:
-            # TODO (erikj): Implement kicks.
-            if target_banned and user_level < ban_level:
-                raise AuthError(
-                    403, "You cannot unban user &s." % (target_user_id,)
-                )
-            elif target_user_id != event.user_id:
-                kick_level = self._get_named_level(auth_events, "kick", 50)
-
-                if user_level < kick_level or user_level <= target_level:
-                    raise AuthError(
-                        403, "You cannot kick user %s." % target_user_id
-                    )
-        elif Membership.BAN == membership:
-            if user_level < ban_level or user_level <= target_level:
-                raise AuthError(403, "You don't have permission to ban")
-        else:
-            raise AuthError(500, "Unknown membership %s" % membership)
-
-        return True
-
-    def _verify_third_party_invite(self, event, auth_events):
-        """
-        Validates that the invite event is authorized by a previous third-party invite.
-
-        Checks that the public key, and keyserver, match those in the third party invite,
-        and that the invite event has a signature issued using that public key.
-
-        Args:
-            event: The m.room.member join event being validated.
-            auth_events: All relevant previous context events which may be used
-                for authorization decisions.
-
-        Return:
-            True if the event fulfills the expectations of a previous third party
-            invite event.
-        """
-        if "third_party_invite" not in event.content:
-            return False
-        if "signed" not in event.content["third_party_invite"]:
-            return False
-        signed = event.content["third_party_invite"]["signed"]
-        for key in {"mxid", "token"}:
-            if key not in signed:
-                return False
-
-        token = signed["token"]
-
-        invite_event = auth_events.get(
-            (EventTypes.ThirdPartyInvite, token,)
-        )
-        if not invite_event:
-            return False
-
-        if invite_event.sender != event.sender:
-            return False
-
-        if event.user_id != invite_event.user_id:
-            return False
-
-        if signed["mxid"] != event.state_key:
-            return False
-        if signed["token"] != token:
-            return False
-
-        for public_key_object in self.get_public_keys(invite_event):
-            public_key = public_key_object["public_key"]
-            try:
-                for server, signature_block in signed["signatures"].items():
-                    for key_name, encoded_signature in signature_block.items():
-                        if not key_name.startswith("ed25519:"):
-                            continue
-                        verify_key = decode_verify_key_bytes(
-                            key_name,
-                            decode_base64(public_key)
-                        )
-                        verify_signed_json(signed, server, verify_key)
-
-                        # We got the public key from the invite, so we know that the
-                        # correct server signed the signed bundle.
-                        # The caller is responsible for checking that the signing
-                        # server has not revoked that public key.
-                        return True
-            except (KeyError, SignatureVerifyException,):
-                continue
-        return False
-
     def get_public_keys(self, invite_event):
-        public_keys = []
-        if "public_key" in invite_event.content:
-            o = {
-                "public_key": invite_event.content["public_key"],
-            }
-            if "key_validity_url" in invite_event.content:
-                o["key_validity_url"] = invite_event.content["key_validity_url"]
-            public_keys.append(o)
-        public_keys.extend(invite_event.content.get("public_keys", []))
-        return public_keys
-
-    def _get_power_level_event(self, auth_events):
-        key = (EventTypes.PowerLevels, "", )
-        return auth_events.get(key)
-
-    def _get_user_power_level(self, user_id, auth_events):
-        power_level_event = self._get_power_level_event(auth_events)
-
-        if power_level_event:
-            level = power_level_event.content.get("users", {}).get(user_id)
-            if not level:
-                level = power_level_event.content.get("users_default", 0)
-
-            if level is None:
-                return 0
-            else:
-                return int(level)
-        else:
-            key = (EventTypes.Create, "", )
-            create_event = auth_events.get(key)
-            if (create_event is not None and
-                    create_event.content["creator"] == user_id):
-                return 100
-            else:
-                return 0
-
-    def _get_named_level(self, auth_events, name, default):
-        power_level_event = self._get_power_level_event(auth_events)
-
-        if not power_level_event:
-            return default
-
-        level = power_level_event.content.get(name, None)
-        if level is not None:
-            return int(level)
-        else:
-            return default
+        return event_auth.get_public_keys(invite_event)
 
     @defer.inlineCallbacks
     def get_user_by_req(self, request, allow_guest=False, rights="access"):
@@ -974,56 +561,6 @@ class Auth(object):
 
         defer.returnValue(auth_ids)
 
-    def _get_send_level(self, etype, state_key, auth_events):
-        key = (EventTypes.PowerLevels, "", )
-        send_level_event = auth_events.get(key)
-        send_level = None
-        if send_level_event:
-            send_level = send_level_event.content.get("events", {}).get(
-                etype
-            )
-            if send_level is None:
-                if state_key is not None:
-                    send_level = send_level_event.content.get(
-                        "state_default", 50
-                    )
-                else:
-                    send_level = send_level_event.content.get(
-                        "events_default", 0
-                    )
-
-        if send_level:
-            send_level = int(send_level)
-        else:
-            send_level = 0
-
-        return send_level
-
-    @log_function
-    def _can_send_event(self, event, auth_events):
-        send_level = self._get_send_level(
-            event.type, event.get("state_key", None), auth_events
-        )
-        user_level = self._get_user_power_level(event.user_id, auth_events)
-
-        if user_level < send_level:
-            raise AuthError(
-                403,
-                "You don't have permission to post that to the room. " +
-                "user_level (%d) < send_level (%d)" % (user_level, send_level)
-            )
-
-        # Check state_key
-        if hasattr(event, "state_key"):
-            if event.state_key.startswith("@"):
-                if event.state_key != event.user_id:
-                    raise AuthError(
-                        403,
-                        "You are not allowed to set others state"
-                    )
-
-        return True
-
     def check_redaction(self, event, auth_events):
         """Check whether the event sender is allowed to redact the target event.
 
@@ -1037,107 +574,7 @@ class Auth(object):
             AuthError if the event sender is definitely not allowed to redact
             the target event.
         """
-        user_level = self._get_user_power_level(event.user_id, auth_events)
-
-        redact_level = self._get_named_level(auth_events, "redact", 50)
-
-        if user_level >= redact_level:
-            return False
-
-        redacter_domain = get_domain_from_id(event.event_id)
-        redactee_domain = get_domain_from_id(event.redacts)
-        if redacter_domain == redactee_domain:
-            return True
-
-        raise AuthError(
-            403,
-            "You don't have permission to redact events"
-        )
-
-    def _check_power_levels(self, event, auth_events):
-        user_list = event.content.get("users", {})
-        # Validate users
-        for k, v in user_list.items():
-            try:
-                UserID.from_string(k)
-            except:
-                raise SynapseError(400, "Not a valid user_id: %s" % (k,))
-
-            try:
-                int(v)
-            except:
-                raise SynapseError(400, "Not a valid power level: %s" % (v,))
-
-        key = (event.type, event.state_key, )
-        current_state = auth_events.get(key)
-
-        if not current_state:
-            return
-
-        user_level = self._get_user_power_level(event.user_id, auth_events)
-
-        # Check other levels:
-        levels_to_check = [
-            ("users_default", None),
-            ("events_default", None),
-            ("state_default", None),
-            ("ban", None),
-            ("redact", None),
-            ("kick", None),
-            ("invite", None),
-        ]
-
-        old_list = current_state.content.get("users")
-        for user in set(old_list.keys() + user_list.keys()):
-            levels_to_check.append(
-                (user, "users")
-            )
-
-        old_list = current_state.content.get("events")
-        new_list = event.content.get("events")
-        for ev_id in set(old_list.keys() + new_list.keys()):
-            levels_to_check.append(
-                (ev_id, "events")
-            )
-
-        old_state = current_state.content
-        new_state = event.content
-
-        for level_to_check, dir in levels_to_check:
-            old_loc = old_state
-            new_loc = new_state
-            if dir:
-                old_loc = old_loc.get(dir, {})
-                new_loc = new_loc.get(dir, {})
-
-            if level_to_check in old_loc:
-                old_level = int(old_loc[level_to_check])
-            else:
-                old_level = None
-
-            if level_to_check in new_loc:
-                new_level = int(new_loc[level_to_check])
-            else:
-                new_level = None
-
-            if new_level is not None and old_level is not None:
-                if new_level == old_level:
-                    continue
-
-            if dir == "users" and level_to_check != event.user_id:
-                if old_level == user_level:
-                    raise AuthError(
-                        403,
-                        "You don't have permission to remove ops level equal "
-                        "to your own"
-                    )
-
-            if old_level > user_level or new_level > user_level:
-                raise AuthError(
-                    403,
-                    "You don't have permission to add ops level greater "
-                    "than your own"
-                )
+        return event_auth.check_redaction(event, auth_events)
 
     @defer.inlineCallbacks
     def check_can_change_room_list(self, room_id, user):
@@ -1167,10 +604,10 @@ class Auth(object):
         if power_level_event:
             auth_events[(EventTypes.PowerLevels, "")] = power_level_event
 
-        send_level = self._get_send_level(
+        send_level = event_auth.get_send_level(
             EventTypes.Aliases, "", auth_events
         )
-        user_level = self._get_user_power_level(user_id, auth_events)
+        user_level = event_auth.get_user_power_level(user_id, auth_events)
 
         if user_level < send_level:
             raise AuthError(
diff --git a/synapse/event_auth.py b/synapse/event_auth.py
new file mode 100644
index 0000000000..983d8e9a85
--- /dev/null
+++ b/synapse/event_auth.py
@@ -0,0 +1,641 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 - 2016 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import logging
+
+from canonicaljson import encode_canonical_json
+from signedjson.key import decode_verify_key_bytes
+from signedjson.sign import verify_signed_json, SignatureVerifyException
+from unpaddedbase64 import decode_base64
+
+from synapse.api.constants import EventTypes, Membership, JoinRules
+from synapse.api.errors import AuthError, SynapseError, EventSizeError
+from synapse.types import UserID, get_domain_from_id
+
+logger = logging.getLogger(__name__)
+
+
+def check(event, auth_events, do_sig_check=True):
+    """ Checks if this event is correctly authed.
+
+    Args:
+        event: the event being checked.
+        auth_events (dict: event-key -> event): the existing room state.
+
+
+    Returns:
+        True if the auth checks pass.
+    """
+    _check_size_limits(event)
+
+    if not hasattr(event, "room_id"):
+        raise AuthError(500, "Event has no room_id: %s" % event)
+
+    if do_sig_check:
+        sender_domain = get_domain_from_id(event.sender)
+        event_id_domain = get_domain_from_id(event.event_id)
+
+        is_invite_via_3pid = (
+            event.type == EventTypes.Member
+            and event.membership == Membership.INVITE
+            and "third_party_invite" in event.content
+        )
+
+        # Check the sender's domain has signed the event
+        if not event.signatures.get(sender_domain):
+            # We allow invites via 3pid to have a sender from a different
+            # HS, as the sender must match the sender of the original
+            # 3pid invite. This is checked further down with the
+            # other dedicated membership checks.
+            if not is_invite_via_3pid:
+                raise AuthError(403, "Event not signed by sender's server")
+
+        # Check the event_id's domain has signed the event
+        if not event.signatures.get(event_id_domain):
+            raise AuthError(403, "Event not signed by sending server")
+
+    if auth_events is None:
+        # Oh, we don't know what the state of the room was, so we
+        # are trusting that this is allowed (at least for now)
+        logger.warn("Trusting event: %s", event.event_id)
+        return True
+
+    if event.type == EventTypes.Create:
+        room_id_domain = get_domain_from_id(event.room_id)
+        if room_id_domain != sender_domain:
+            raise AuthError(
+                403,
+                "Creation event's room_id domain does not match sender's"
+            )
+        # FIXME
+        return True
+
+    creation_event = auth_events.get((EventTypes.Create, ""), None)
+
+    if not creation_event:
+        raise SynapseError(
+            403,
+            "Room %r does not exist" % (event.room_id,)
+        )
+
+    creating_domain = get_domain_from_id(event.room_id)
+    originating_domain = get_domain_from_id(event.sender)
+    if creating_domain != originating_domain:
+        if not _can_federate(event, auth_events):
+            raise AuthError(
+                403,
+                "This room has been marked as unfederatable."
+            )
+
+    # FIXME: Temp hack
+    if event.type == EventTypes.Aliases:
+        if not event.is_state():
+            raise AuthError(
+                403,
+                "Alias event must be a state event",
+            )
+        if not event.state_key:
+            raise AuthError(
+                403,
+                "Alias event must have non-empty state_key"
+            )
+        sender_domain = get_domain_from_id(event.sender)
+        if event.state_key != sender_domain:
+            raise AuthError(
+                403,
+                "Alias event's state_key does not match sender's domain"
+            )
+        return True
+
+    logger.debug(
+        "Auth events: %s",
+        [a.event_id for a in auth_events.values()]
+    )
+
+    if event.type == EventTypes.Member:
+        allowed = _is_membership_change_allowed(
+            event, auth_events
+        )
+        if allowed:
+            logger.debug("Allowing! %s", event)
+        else:
+            logger.debug("Denying! %s", event)
+        return allowed
+
+    _check_event_sender_in_room(event, auth_events)
+
+    # Special case to allow m.room.third_party_invite events wherever
+    # a user is allowed to issue invites.  Fixes
+    # https://github.com/vector-im/vector-web/issues/1208 hopefully
+    if event.type == EventTypes.ThirdPartyInvite:
+        user_level = get_user_power_level(event.user_id, auth_events)
+        invite_level = _get_named_level(auth_events, "invite", 0)
+
+        if user_level < invite_level:
+            raise AuthError(
+                403, (
+                    "You cannot issue a third party invite for %s." %
+                    (event.content.display_name,)
+                )
+            )
+        else:
+            return True
+
+    _can_send_event(event, auth_events)
+
+    if event.type == EventTypes.PowerLevels:
+        _check_power_levels(event, auth_events)
+
+    if event.type == EventTypes.Redaction:
+        check_redaction(event, auth_events)
+
+    logger.debug("Allowing! %s", event)
+
+
+def _check_size_limits(event):
+    def too_big(field):
+        raise EventSizeError("%s too large" % (field,))
+
+    if len(event.user_id) > 255:
+        too_big("user_id")
+    if len(event.room_id) > 255:
+        too_big("room_id")
+    if event.is_state() and len(event.state_key) > 255:
+        too_big("state_key")
+    if len(event.type) > 255:
+        too_big("type")
+    if len(event.event_id) > 255:
+        too_big("event_id")
+    if len(encode_canonical_json(event.get_pdu_json())) > 65536:
+        too_big("event")
+
+
+def _can_federate(event, auth_events):
+    creation_event = auth_events.get((EventTypes.Create, ""))
+
+    return creation_event.content.get("m.federate", True) is True
+
+
+def _is_membership_change_allowed(event, auth_events):
+    membership = event.content["membership"]
+
+    # Check if this is the room creator joining:
+    if len(event.prev_events) == 1 and Membership.JOIN == membership:
+        # Get room creation event:
+        key = (EventTypes.Create, "", )
+        create = auth_events.get(key)
+        if create and event.prev_events[0][0] == create.event_id:
+            if create.content["creator"] == event.state_key:
+                return True
+
+    target_user_id = event.state_key
+
+    creating_domain = get_domain_from_id(event.room_id)
+    target_domain = get_domain_from_id(target_user_id)
+    if creating_domain != target_domain:
+        if not _can_federate(event, auth_events):
+            raise AuthError(
+                403,
+                "This room has been marked as unfederatable."
+            )
+
+    # get info about the caller
+    key = (EventTypes.Member, event.user_id, )
+    caller = auth_events.get(key)
+
+    caller_in_room = caller and caller.membership == Membership.JOIN
+    caller_invited = caller and caller.membership == Membership.INVITE
+
+    # get info about the target
+    key = (EventTypes.Member, target_user_id, )
+    target = auth_events.get(key)
+
+    target_in_room = target and target.membership == Membership.JOIN
+    target_banned = target and target.membership == Membership.BAN
+
+    key = (EventTypes.JoinRules, "", )
+    join_rule_event = auth_events.get(key)
+    if join_rule_event:
+        join_rule = join_rule_event.content.get(
+            "join_rule", JoinRules.INVITE
+        )
+    else:
+        join_rule = JoinRules.INVITE
+
+    user_level = get_user_power_level(event.user_id, auth_events)
+    target_level = get_user_power_level(
+        target_user_id, auth_events
+    )
+
+    # FIXME (erikj): What should we do here as the default?
+    ban_level = _get_named_level(auth_events, "ban", 50)
+
+    logger.debug(
+        "_is_membership_change_allowed: %s",
+        {
+            "caller_in_room": caller_in_room,
+            "caller_invited": caller_invited,
+            "target_banned": target_banned,
+            "target_in_room": target_in_room,
+            "membership": membership,
+            "join_rule": join_rule,
+            "target_user_id": target_user_id,
+            "event.user_id": event.user_id,
+        }
+    )
+
+    if Membership.INVITE == membership and "third_party_invite" in event.content:
+        if not _verify_third_party_invite(event, auth_events):
+            raise AuthError(403, "You are not invited to this room.")
+        if target_banned:
+            raise AuthError(
+                403, "%s is banned from the room" % (target_user_id,)
+            )
+        return True
+
+    if Membership.JOIN != membership:
+        if (caller_invited
+                and Membership.LEAVE == membership
+                and target_user_id == event.user_id):
+            return True
+
+        if not caller_in_room:  # caller isn't joined
+            raise AuthError(
+                403,
+                "%s not in room %s." % (event.user_id, event.room_id,)
+            )
+
+    if Membership.INVITE == membership:
+        # TODO (erikj): We should probably handle this more intelligently
+        # PRIVATE join rules.
+
+        # Invites are valid iff caller is in the room and target isn't.
+        if target_banned:
+            raise AuthError(
+                403, "%s is banned from the room" % (target_user_id,)
+            )
+        elif target_in_room:  # the target is already in the room.
+            raise AuthError(403, "%s is already in the room." %
+                                 target_user_id)
+        else:
+            invite_level = _get_named_level(auth_events, "invite", 0)
+
+            if user_level < invite_level:
+                raise AuthError(
+                    403, "You cannot invite user %s." % target_user_id
+                )
+    elif Membership.JOIN == membership:
+        # Joins are valid iff caller == target and they were:
+        # invited: They are accepting the invitation
+        # joined: It's a NOOP
+        if event.user_id != target_user_id:
+            raise AuthError(403, "Cannot force another user to join.")
+        elif target_banned:
+            raise AuthError(403, "You are banned from this room")
+        elif join_rule == JoinRules.PUBLIC:
+            pass
+        elif join_rule == JoinRules.INVITE:
+            if not caller_in_room and not caller_invited:
+                raise AuthError(403, "You are not invited to this room.")
+        else:
+            # TODO (erikj): may_join list
+            # TODO (erikj): private rooms
+            raise AuthError(403, "You are not allowed to join this room")
+    elif Membership.LEAVE == membership:
+        # TODO (erikj): Implement kicks.
+        if target_banned and user_level < ban_level:
+            raise AuthError(
+                403, "You cannot unban user &s." % (target_user_id,)
+            )
+        elif target_user_id != event.user_id:
+            kick_level = _get_named_level(auth_events, "kick", 50)
+
+            if user_level < kick_level or user_level <= target_level:
+                raise AuthError(
+                    403, "You cannot kick user %s." % target_user_id
+                )
+    elif Membership.BAN == membership:
+        if user_level < ban_level or user_level <= target_level:
+            raise AuthError(403, "You don't have permission to ban")
+    else:
+        raise AuthError(500, "Unknown membership %s" % membership)
+
+    return True
+
+
+def _check_event_sender_in_room(event, auth_events):
+    key = (EventTypes.Member, event.user_id, )
+    member_event = auth_events.get(key)
+
+    return _check_joined_room(
+        member_event,
+        event.user_id,
+        event.room_id
+    )
+
+
+def _check_joined_room(member, user_id, room_id):
+    if not member or member.membership != Membership.JOIN:
+        raise AuthError(403, "User %s not in room %s (%s)" % (
+            user_id, room_id, repr(member)
+        ))
+
+
+def get_send_level(etype, state_key, auth_events):
+    key = (EventTypes.PowerLevels, "", )
+    send_level_event = auth_events.get(key)
+    send_level = None
+    if send_level_event:
+        send_level = send_level_event.content.get("events", {}).get(
+            etype
+        )
+        if send_level is None:
+            if state_key is not None:
+                send_level = send_level_event.content.get(
+                    "state_default", 50
+                )
+            else:
+                send_level = send_level_event.content.get(
+                    "events_default", 0
+                )
+
+    if send_level:
+        send_level = int(send_level)
+    else:
+        send_level = 0
+
+    return send_level
+
+
+def _can_send_event(event, auth_events):
+    send_level = get_send_level(
+        event.type, event.get("state_key", None), auth_events
+    )
+    user_level = get_user_power_level(event.user_id, auth_events)
+
+    if user_level < send_level:
+        raise AuthError(
+            403,
+            "You don't have permission to post that to the room. " +
+            "user_level (%d) < send_level (%d)" % (user_level, send_level)
+        )
+
+    # Check state_key
+    if hasattr(event, "state_key"):
+        if event.state_key.startswith("@"):
+            if event.state_key != event.user_id:
+                raise AuthError(
+                    403,
+                    "You are not allowed to set others state"
+                )
+
+    return True
+
+
+def check_redaction(event, auth_events):
+    """Check whether the event sender is allowed to redact the target event.
+
+    Returns:
+        True if the the sender is allowed to redact the target event if the
+        target event was created by them.
+        False if the sender is allowed to redact the target event with no
+        further checks.
+
+    Raises:
+        AuthError if the event sender is definitely not allowed to redact
+        the target event.
+    """
+    user_level = get_user_power_level(event.user_id, auth_events)
+
+    redact_level = _get_named_level(auth_events, "redact", 50)
+
+    if user_level >= redact_level:
+        return False
+
+    redacter_domain = get_domain_from_id(event.event_id)
+    redactee_domain = get_domain_from_id(event.redacts)
+    if redacter_domain == redactee_domain:
+        return True
+
+    raise AuthError(
+        403,
+        "You don't have permission to redact events"
+    )
+
+
+def _check_power_levels(event, auth_events):
+    user_list = event.content.get("users", {})
+    # Validate users
+    for k, v in user_list.items():
+        try:
+            UserID.from_string(k)
+        except:
+            raise SynapseError(400, "Not a valid user_id: %s" % (k,))
+
+        try:
+            int(v)
+        except:
+            raise SynapseError(400, "Not a valid power level: %s" % (v,))
+
+    key = (event.type, event.state_key, )
+    current_state = auth_events.get(key)
+
+    if not current_state:
+        return
+
+    user_level = get_user_power_level(event.user_id, auth_events)
+
+    # Check other levels:
+    levels_to_check = [
+        ("users_default", None),
+        ("events_default", None),
+        ("state_default", None),
+        ("ban", None),
+        ("redact", None),
+        ("kick", None),
+        ("invite", None),
+    ]
+
+    old_list = current_state.content.get("users")
+    for user in set(old_list.keys() + user_list.keys()):
+        levels_to_check.append(
+            (user, "users")
+        )
+
+    old_list = current_state.content.get("events")
+    new_list = event.content.get("events")
+    for ev_id in set(old_list.keys() + new_list.keys()):
+        levels_to_check.append(
+            (ev_id, "events")
+        )
+
+    old_state = current_state.content
+    new_state = event.content
+
+    for level_to_check, dir in levels_to_check:
+        old_loc = old_state
+        new_loc = new_state
+        if dir:
+            old_loc = old_loc.get(dir, {})
+            new_loc = new_loc.get(dir, {})
+
+        if level_to_check in old_loc:
+            old_level = int(old_loc[level_to_check])
+        else:
+            old_level = None
+
+        if level_to_check in new_loc:
+            new_level = int(new_loc[level_to_check])
+        else:
+            new_level = None
+
+        if new_level is not None and old_level is not None:
+            if new_level == old_level:
+                continue
+
+        if dir == "users" and level_to_check != event.user_id:
+            if old_level == user_level:
+                raise AuthError(
+                    403,
+                    "You don't have permission to remove ops level equal "
+                    "to your own"
+                )
+
+        if old_level > user_level or new_level > user_level:
+            raise AuthError(
+                403,
+                "You don't have permission to add ops level greater "
+                "than your own"
+            )
+
+
+def _get_power_level_event(auth_events):
+    key = (EventTypes.PowerLevels, "", )
+    return auth_events.get(key)
+
+
+def get_user_power_level(user_id, auth_events):
+    power_level_event = _get_power_level_event(auth_events)
+
+    if power_level_event:
+        level = power_level_event.content.get("users", {}).get(user_id)
+        if not level:
+            level = power_level_event.content.get("users_default", 0)
+
+        if level is None:
+            return 0
+        else:
+            return int(level)
+    else:
+        key = (EventTypes.Create, "", )
+        create_event = auth_events.get(key)
+        if (create_event is not None and
+                create_event.content["creator"] == user_id):
+            return 100
+        else:
+            return 0
+
+
+def _get_named_level(auth_events, name, default):
+    power_level_event = _get_power_level_event(auth_events)
+
+    if not power_level_event:
+        return default
+
+    level = power_level_event.content.get(name, None)
+    if level is not None:
+        return int(level)
+    else:
+        return default
+
+
+def _verify_third_party_invite(event, auth_events):
+    """
+    Validates that the invite event is authorized by a previous third-party invite.
+
+    Checks that the public key, and keyserver, match those in the third party invite,
+    and that the invite event has a signature issued using that public key.
+
+    Args:
+        event: The m.room.member join event being validated.
+        auth_events: All relevant previous context events which may be used
+            for authorization decisions.
+
+    Return:
+        True if the event fulfills the expectations of a previous third party
+        invite event.
+    """
+    if "third_party_invite" not in event.content:
+        return False
+    if "signed" not in event.content["third_party_invite"]:
+        return False
+    signed = event.content["third_party_invite"]["signed"]
+    for key in {"mxid", "token"}:
+        if key not in signed:
+            return False
+
+    token = signed["token"]
+
+    invite_event = auth_events.get(
+        (EventTypes.ThirdPartyInvite, token,)
+    )
+    if not invite_event:
+        return False
+
+    if invite_event.sender != event.sender:
+        return False
+
+    if event.user_id != invite_event.user_id:
+        return False
+
+    if signed["mxid"] != event.state_key:
+        return False
+    if signed["token"] != token:
+        return False
+
+    for public_key_object in get_public_keys(invite_event):
+        public_key = public_key_object["public_key"]
+        try:
+            for server, signature_block in signed["signatures"].items():
+                for key_name, encoded_signature in signature_block.items():
+                    if not key_name.startswith("ed25519:"):
+                        continue
+                    verify_key = decode_verify_key_bytes(
+                        key_name,
+                        decode_base64(public_key)
+                    )
+                    verify_signed_json(signed, server, verify_key)
+
+                    # We got the public key from the invite, so we know that the
+                    # correct server signed the signed bundle.
+                    # The caller is responsible for checking that the signing
+                    # server has not revoked that public key.
+                    return True
+        except (KeyError, SignatureVerifyException,):
+            continue
+    return False
+
+
+def get_public_keys(invite_event):
+    public_keys = []
+    if "public_key" in invite_event.content:
+        o = {
+            "public_key": invite_event.content["public_key"],
+        }
+        if "key_validity_url" in invite_event.content:
+            o["key_validity_url"] = invite_event.content["key_validity_url"]
+        public_keys.append(o)
+    public_keys.extend(invite_event.content.get("public_keys", []))
+    return public_keys