Clarify server status options

[richsalz]

Three ways for a server to send CT data. Clarify when and how each is used.

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[sleevi]

Thanks Rich for sending this.

Unfortunately, I don’t believe it is accurate or reflecting implementation experience to suggest the TLS 1.3 mechanism is preferred. The design of CT, and the ample implementation experience of both CAs and site operators, firmly supports embedded proofs as the preferred mechanism. This reduces server-side complexity and overhead for the general case (e.g. every TLS server having to manage the state of every UAs set of accepted Logs and required policies and appropriately ensure the necessary SCTs are sent).

It remains a quite nice option for CDNs who are staffed to ensure such things, just as they do with certificate and certificate chains, but I think it’s rather the opposite: the TLS and OCSP mechanisms are less preferred because they have high operational complexity, ongoing maintenance costs (since the SCTs must continue to comply with policy, as opposed to issuance-date policies that embedded SCTs have), and create a more fragile, less agile ecosystem.

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[richsalz]

Push commit to address comments from @robstradling and @sleevi

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[richsalz]

I pushed a commit that fixes the three typo's @robstradling found.

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