Nice tool! Looks like a great solution.

But unfortunately I don't have it in a random docker/kubernetes containers or random internal servers, and these are the contexts where I personally usually want to check my external IP. They usually have curl though.

Maybe curl ought to support STUN (if it doesn't already). It's becoming a very common technology now that NAT is so prevalent.

Because one requires you to merely type a simple URL in your browser that you already likely have open, the other requires you to install Go, clone a git repo, compile the program, install the program, and THEN finally run the program.

... only to be blocked by the corporate firewall which doesn't allow anything besides tcp/80 and tcp/443.

This is very cool and something that'd be neat to roll into a toolset. But I think you're missing the point of izanhazip. It's meant to be quick and easily accessible regardless of where you are or what system you're on (assuming there's curl or similar installed).

I might not have permission or it wouldn't be reasonable to install something. And I can link it to customers or give them a simple command to run, and all it returns is the actual info I need from them.