Replace SimpleJson

[DavidBoike]

The SimpleJson codebase is not maintained and is fairly old. This constitutes a maintenance risk, and while there are no known vulnerabilities, if there ever were any detected, it's unlikely there would be a fix.

It should be possible to replace SimpleJson, perhaps with System.Text.Json, although some migration may be required.

[kbaley]

See also:

• Create new JSON message serializer using System.Text.Json NServiceBus#6577