On my server, I've added metadata->spdx to show the software licence used by the server.
See https://example.viii.fi/nodeinfo/2.1 for an example.

Would it be sensible to formally add this to the "software" section instead? Something like:

 "software": {
    "name": "Cool AP Server",
    "version": "1.23",
    "repository": "https://example.com/",
    "SPDX-License-Identifier: "MIT"
  },

Ref: https://spdx.dev/learn/handling-license-info/