Unable to setup cross-signing keys about element-android

[hardcore-sushi]

This issue actually affects more that just the reset cross-signing key feature.

If the first login to the account is made with Element (typically when registering), it sends the same request to configure the initial cross-signing keys. Due to the malformed request payload, the setup fails, although Element reports it as properly enabled in the settings. Consequently, the session is reported as not verified (red shield) in encrypted chats, and any keys verification with other accounts is thus prevented.

For people stumbled upon this issue and looking for a workaround, you can add a rule in your nginx reverse proxy (if you use one) to fix the JSON payload. You need lua support with the cjson library. Here is an example configuration snippet:

location = /_matrix/client/unstable/keys/device_signing/upload {
  if ($request_method = POST) {
    access_by_lua_block {
      local cjson = require "cjson"
      ngx.req.read_body()
      local data = cjson.decode(ngx.req.get_body_data())
      if data["auth"] ~= nil and data.auth["user"] ~= nil then
        data.auth.identifier = {
          type = "m.id.user",
          user = data.auth.user,
        };
        ngx.req.set_body_data(cjson.encode(data))
      end
    }
  }
  proxy_pass http://<CONDUIT ENDPOINT>$request_uri;
  # ...
}