Validate JSON files when they are being uploaded against a JSON schema

[simon-wacker]

There are some problems:

1. If the schema is not available offline it needs to be downloaded. A downloaded schema can reference other schemas by URIs. These URIs need not be resolvable according to https://json-schema.org/draft/2020-12/json-schema-core#section-8.2.3 It is therefore unknown in general where to download these referenced schemas.
2. The library I decided to use, namely https://github.com/json-everything/json-everything, supports the downloads of external references but advices against it in https://docs.json-everything.net/schema/examples/external-schemas/#example-schema-fetching And the fetching mechanism is non-async even though it is definitely an async operation. I worked around it by using Task.Wait() and Task.Result whose usage is strongly discouraged by Microsoft.
3. The library json-everything seems to be poorly maintained, in particular, documentation is outdated.

Possible solutions:

1. Download schemata in advance semi-manually and safe them. How do we handle multiple versions then? And how do we keep it up to date?
2. Find a better library ... A possible alternative may be https://github.com/RicoSuter/NJsonSchema