Should be a PreAuthenticationProvider.
Note ConfirmEdit currently really doesn't play nice with the AuthManager WIP code, because the new ApiAMCreateAccount (and probably ApiClientLogin too) isn't recognized by ConfirmEdit to do its parameters but still is going to hit its hooks on AbortNewAccount (and probably AbortLogin too).
AuthManager-enabled core + ReCaptcha does not work, with or without that patch. Non-AuthManager-enabled core + any captcha with the patch should work, although I only tested a few combinations.
Not a blocker for WMF deployment but it's bundled with the tarball so it needs to be done before the final 1.27 release. I have a half-baked patch for ReCaptcha but I figured it makes more sense to work on the WMF-deployed extensions first, since that blocks testing in production.