Signed JSON example using JWS

[anweiss]

Committer Notes

Signed JSON example using JWS. This is the signed rendition of NIST_SP-800-53_rev4_catalog.json. Generated using the latest iteration of oscalkit. Leverages the go-jose library and was signed using the test keys provided by that library. The signing algorithm used was RSASSA-PKCS-v1.5 using SHA-512.

This supports #245 but merely serves as a prototype for the use of JWS for signing OSCAL JSON documents as we have yet to come to a consensus on a signing solution for JSON.

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[david-waltermire]

Closing this one for now. We can reconsider this once more work is done on #245.