use User ID type in OlmPayload and DeviceKeys (#2412)

* use User ID type in OlmPayload and DeviceKeys

Signed-off-by: Johanna Stuber <johannas@element.io>

* add newsfragment

Signed-off-by: Johanna Stuber <johannas@element.io>

---------

Signed-off-by: Johanna Stuber <johannas@element.io>

changelogs/client_server/newsfragments/2404.breaking

@@ -0,0 +1 @@
+Clients are now supposed to follow 30x redirects from `/.well-known/matrix/client` as per [MSC4402](https://github.com/matrix-org/matrix-spec-proposals/pull/4402).

changelogs/client_server/newsfragments/2412.clarification

@@ -0,0 +1 @@
+Use the User ID type in OlmPayload and DeviceKeys.

changelogs/client_server/newsfragments/2417.clarification

@@ -0,0 +1 @@
+Wording improvements and spelling fixes. Contributed by @HarHarLinks.

content/client-server-api/_index.md

@@ -429,6 +429,7 @@ Instead, they can be reached via HTTPS on the [server name](/appendices/#server-
 
 Servers hosting the `.well-known` JSON file SHOULD offer CORS headers,
 as per the [CORS](#web-browser-clients) section in this specification.
+{{% added-in v="1.20" %}} Servers SHOULD also ensure that each 30x redirect, if any, offers such CORS headers.
 {{% /boxes/note %}}
 
 The flow for auto-discovery is as follows:
@@ -437,6 +438,7 @@ The flow for auto-discovery is as follows:
     Matrix ID at the first colon.
 2.  Extract the hostname from the server name as described by the [grammar](/appendices/#server-name).
 3.  Make a GET request to `https://hostname/.well-known/matrix/client`.
+    {{% added-in v="1.20" %}} 30x redirects SHOULD be followed, however redirection loops should be avoided.
     1.  If the returned status code is 404, then `IGNORE`.
     2.  If the returned status code is not 200, or the response body is
         empty, then `FAIL_PROMPT`.
@@ -3660,7 +3662,7 @@ The actual aggregation format depends on the `rel_type`.
 
 When an event is served to the client through the APIs listed below, a
 `m.relations` property is included under `unsigned` if the event has child
-events which can be aggregated and point at it. The `m.relations` property is
+events which can be aggregated. The `m.relations` property is
 an object keyed by `rel_type` and value being the type-specific aggregated
 format for that `rel_type`. This `m.relations` property is known as a "bundled
 aggregation".

content/client-server-api/modules/threading.md

@@ -191,7 +191,7 @@ Note that, as in the example above, child events of the `latest_event` should
 themselves be aggregated and included under `m.relations` for that event. The
 server should be careful to avoid loops, though loops are not currently
 possible due to `m.thread` not being permitted to target an event with an
-`m.relates_to` property.
+`m.relates_to` property with a `rel_type`.
 
 `count` is simply the number of events using `m.thread` as a `rel_type` pointing to the target event.
 It does not include events sent by [ignored users](#ignoring-users).

data/api/client-server/definitions/device_keys.yaml

@@ -20,6 +20,8 @@ properties:
     description: |-
       The ID of the user the device belongs to. Must match the user ID used
       when logging in.
+    format: mx-user-id
+    pattern: "^@"
     example: "@alice:example.com"
   device_id:
     type: string

data/api/client-server/definitions/olm_payload.yaml

@@ -27,9 +27,13 @@ properties:
   sender:
     type: string
     description: The user ID of the event sender.
+    format: mx-user-id
+    pattern: "^@"
   recipient:
     type: string
     description: The user ID of the intended event recipient.
+    format: mx-user-id
+    pattern: "^@"
   recipient_keys:
     description: The recipient's signing keys of the encrypted event.
     $ref: "#/components/schemas/SigningKeys"

data/api/client-server/wellknown.yaml

@@ -1,4 +1,5 @@
 # Copyright 2018 New Vector Ltd
+# Copyright 2026 Hagen Echzell
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -20,7 +21,11 @@ paths:
     get:
       summary: Gets Matrix server discovery information about the domain.
       description: |-
-        Gets discovery information about the domain. The file may include
+        Gets discovery information about the domain.
+        {{% added-in v="1.20" %}} Clients SHOULD follow 30x redirects, carefully
+        avoiding redirect loops, and use normal X.509 certificate validation.
+        
+        The file may include
         additional keys, which MUST follow the Java package naming convention,
         e.g. `com.example.myapp.property`. This ensures property names are
         suitably namespaced for each application and reduces the risk of