For option (d) of #1405.
For an HTTPS request of /bootstrap-dns, this returns e.g.:
{
"log.tailscale.io": [
"2600:1f14:436:d603:342:4c0d:2df9:191b",
"34.210.105.16"
],
"login.tailscale.com": [
"2a05:d014:386:203:f8b4:1d5a:f163:e187",
"3.121.18.47"
]
}
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>