reCaptcha integration with IDPv3

[Cantor, Scott]

> I think the "riskier" aspect is the manipulation of the context tree in that
> particular way. That isn't public. In the scheme of things, that's pretty unlikely
> to change. But no, I can't promise it.

Of course, there's the other option: give us a contributed patch to add the feature to the code for the next version. A substantial feature would have to be Apache-licensed or made under our contribution agreement, though.

-- Scott