cli client does not work on IPv6 nodes

I don't have any native IPv4, though my network does have NAT64 (which provides access to the entire IPv4 internet).

However, keybase does not seem to attempt to establish a connection over IPv6:

$ keybase signup
warn: No config file found; tried '/home/hugo/.config/keybase/config.json'
Your email: hugo@barrera.io
Invitation code (leave blank if you don't have one): 
Would you like to be added to the invite list? [Y/n] Y
Your name: Hugo Osvaldo Barrera
Any comments for the team: 
error: Could not access URL: https://api.keybase.io:443/_/api/1.0/invitation_request.json

In this day and age, IPv6 support is critical.

Note that this network has NAT64, so the remote server does not require any knowledge of IPv6, but the client should attempt to connect to relevant AAAA records as wel as A records when initiating the connection.

Start by reproducing the failure with keybase signup on an IPv6-only or NAT64 network and observe the request to https://api.keybase.io:443/_/api/1.0/invitation_request.json. Trace the CLI's connection path and verify how it handles A and AAAA records. Done means the client can establish the request over IPv6 when IPv4 is unavailable.