From 1a807dfe6855b15d8574eb92541dd84b946f16bd Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Mon, 8 Jul 2019 14:19:39 +0100
Subject: [PATCH 1/3] Use application/json when querying the IS's /store-invite
 endpoint

---
 synapse/handlers/room_member.py | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 4d6e883802..b050967b8f 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -29,7 +29,7 @@ from twisted.internet import defer
 import synapse.server
 import synapse.types
 from synapse.api.constants import EventTypes, Membership
-from synapse.api.errors import AuthError, Codes, SynapseError
+from synapse.api.errors import AuthError, Codes, HttpResponseException, SynapseError
 from synapse.types import RoomID, UserID
 from synapse.util.async_helpers import Linearizer
 from synapse.util.distributor import user_joined_room, user_left_room
@@ -904,9 +904,22 @@ class RoomMemberHandler(object):
                 }
             )
 
-        data = yield self.simple_http_client.post_urlencoded_get_json(
-            is_url, invite_config
-        )
+        try:
+            data = yield self.simple_http_client.post_json_get_json(
+                is_url, invite_config
+            )
+        except HttpResponseException as e:
+            # Some identity servers may only support application/x-www-form-urlencoded
+            # types. This is especially true with old instances of Sydent, see
+            # https://github.com/matrix-org/sydent/pull/170
+            logger.info(
+                "Failed to POST %s with JSON, falling back to urlencoded form: %s",
+                is_url, e,
+            )
+            data = yield self.simple_http_client.post_urlencoded_get_json(
+                is_url, invite_config
+            )
+
         # TODO: Check for success
         token = data["token"]
         public_keys = data.get("public_keys", [])

From f05c7d62bc2bb504f0048adf6e68decdbe31f80d Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Mon, 8 Jul 2019 14:29:27 +0100
Subject: [PATCH 2/3] Lint

---
 synapse/handlers/room_member.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index b050967b8f..c3420b4b22 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -914,7 +914,8 @@ class RoomMemberHandler(object):
             # https://github.com/matrix-org/sydent/pull/170
             logger.info(
                 "Failed to POST %s with JSON, falling back to urlencoded form: %s",
-                is_url, e,
+                is_url,
+                e,
             )
             data = yield self.simple_http_client.post_urlencoded_get_json(
                 is_url, invite_config

From c142e5d16ad4dc5a4cbc93d7d19b2902be72644b Mon Sep 17 00:00:00 2001
From: Brendan Abolivier <babolivier@matrix.org>
Date: Mon, 8 Jul 2019 14:29:37 +0100
Subject: [PATCH 3/3] Changelog

---
 changelog.d/5638.bugfix | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/5638.bugfix

diff --git a/changelog.d/5638.bugfix b/changelog.d/5638.bugfix
new file mode 100644
index 0000000000..66781ad9e6
--- /dev/null
+++ b/changelog.d/5638.bugfix
@@ -0,0 +1 @@
+Fix requests to the `/store_invite` endpoint of identity servers being sent in the wrong format.