Unable to listen on ipv6 - unable to authenticate

[thoro]

Describe the issue

Kubelogin does not listen on IPv6, therefore it's sometimes impossible to authenticate, if localhost is resolved to ipv6 and a preferred way to connect.

To reproduce

try to login on a ipv6 first machine, curl will get stuck

Your environment

• OS: macOS
• kubelogin version: v1.28.1 via brew
• kubectl version: 1.30.2
• OpenID Connect provider: Azure / Dex

[thoro]

Figured out why it's happening for me.

So I have another app that listens on *:8000 and kubelogin only listens to 127.0.0.1:8000, so the IPv6 request is forwarded to the *:8000 app, which blocks the http request and the failback to ipv4 can never work.

[lwille]

This is also an issue when using Brave, which seems to resolve localhost to ::1 and only that.
Kubelogin rejects a listen-address with more than one :.

[ePaul]

A workaround might be to pick a port which is free on both TCP 4 and TCP 6, and listen on that one.

for p in 8000 18000 28000 38000
do
  if ! netstat -ltn | fgrep ':'$p -q
  then
     kubelogin ... --listen-address localhost:$p
     break
  fi
done