Page Comparison

Explain that first factor is up to you as to how you want to implement it.

Sequence Diagram 

dictionary PreSignObtainU2fRequest {
  DOMString type;
  DOMString username; // TODO(mirko): need to get this another way.
};

type of type  of type DOMString

The type of

...

U2F Request to obtain is either "pre_sign" or "pre_enroll".

username of type  of type DOMString

The username to obtain a

...

Request for. This needs to be authenticated instead.

The response is a U2F Request dictionary dictionary. (see fido-u2f-javascript-api; 3.1.1 Dictionary Request Members)