Why are various predefined extensions defined as extensions, and not just parts of the spec?

[bzbarsky]

Is this because they are allowed to not be supported?

[equalsJeffH]

yes. [ e.g., see https://lists.w3.org/Archives/Public/public-webauthn/2016Sep/0110.html ]

[selfissued]

As we discussed in the F2F, it's a business decision which extensions to support. They're extensions because supporting them is optional.

FYI, #386 should make it a lot clearer how to define and register new extensions. It makes it clear that the initially defined ones are not somehow "special".

[equalsJeffH]

Overall, a +1 to @selfissued's (mike jones) explanation, although to be fair, there are arguments that some of the "extensions" should not be "extensions" and should be incorporated directly into the spec. Rolf @rlin1 made this point in the last F2F.

[selfissued]

I believe that this issue asked a question that has been answered and proposes no changes to the specification. I am therefore closing it on this basis. New issues can be filed that do propose specific changes, if desired.