Out-of-band challenge

[bifurcation]

We need a challenge type to cover types of validation that can't be done automatically, in band to ACME. For example, a CA doing OV or EV validation might need the applicant to upload some documents through a web form. We should add a generic "out-of-band" challenge type that has a URL for a web site where the applicant gan go for instructions. I think the challenge object would look something like:

{
  "type": "out-of-band",
  "url": "https://example.com/papers-please"
}

There would be no response object; you just click the link, and when you complete the instructions there, the CA reflects this in the "status" field of the challenge object.

[ebekker]

A few months back I wrote up a proposal for this idea -- the hope is that ACME could evolve to become the language that all cert issuers talk to support a standard for cert management and exchange.

[hardie]

At IETF 95, agreed that this seemed reasonable to pursue, but needs to have a PR that describes what the URI characteristics are.