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Spec for MSC4402: Consistent redirects for .well-known-files #2404

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Spec for MSC4402: Consistent redirects for .well-known-files #2404

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c796f35
Spec for MSC4402: Consistent redirects for .well-known-files
derhagen Jun 22, 2026
2a80641
Add changelog file
derhagen Jun 23, 2026
60df211
Indicate spec version for changes
derhagen Jun 25, 2026
f33aaa1
Capitalize some `should`s
derhagen Jun 25, 2026
a04a046
Increment added-in spec version after release of 1.19
derhagen Jul 9, 2026
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1 change: 1 addition & 0 deletions changelogs/client_server/newsfragments/2404.breaking
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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).
2 changes: 2 additions & 0 deletions content/client-server-api/_index.md
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Expand Up @@ -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:
Expand All @@ -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`.
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7 changes: 6 additions & 1 deletion data/api/client-server/wellknown.yaml
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# 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.
Expand All @@ -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
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