RFE: expose valid signing_intent choices to clients

Clients can send a signing_intent argument to buildContainer tasks. Is there any way for clients programmatically discover a list of valid options for that field?

I see the signing intents are defined in https://osbs.readthedocs.io/en/latest/admins.html#server-side-configuration-for-atomic-reactor , but is there any way for me to read that information as a non-administrator client?

The rpkg CLI has a --signing-intent argument, but rpkg container-build --help does not show the list of possible choices.

koji --noauth call system.methodHelp buildContainer gives me the API doc for the buildContainer task, but that text says to read builder_containerbuild.py. The JSON Schema in PARAMS_SCHEMA in that file says:

"signing_intent": {
    "type": ["string", "null"],
    "description": "Signing intent of the ODCS composes."
},

So this string could be anything, and clients have to guess and check at the correct values, or learn it through some other form of tribal knowledge.

[ktdreyer]

How about this change to the JSON schema? https://github.com/containerbuildsystem/atomic-reactor/issues/1552

[ktdreyer]

And I put this into rpkg’ --help text also, https://pagure.io/rpkg/pull-request/565