Backwards compatible `payloadType` should be an exact match

[secure-systems-lab]

Backwards compatible `payloadType` should be an exact match

[MarkLodato]

Good point about the URI for documentation purposes. One downside is that if we pick, say "in-toto.io/backwards-compatible-json" as the magic string, and then the domain changes in 5 years (say because of a TLD change or a project name change or whatever) then we're stuck with this historical URI. But I suppose that isn't a huge deal.

I'll send a PR.

[trishankatdatadog]

Agree with the exact match of payloadType.

I think it's helpful to make it a URI so that curious readers can look up more information about custom payload types, if interested. Optionality without breaking security (so long as machine clients don't open or parse these URLs automatically for whatever reason).

[MarkLodato]

Then again, this is specifically about in-toto and TUF backwards compatibility, so I suppose that URI actually does make sense. :)