[BUG] Claude is no longer able to sign-in into a website not even locally

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

When claude takes over my browser in chrome with the extension, it used to be able to sign in with a provided user. Especially for me a web developer this is super handy to verify multiple cases with users that have different permissions.

Only this stopped working, i get that this would not work for the public web, on the other side... im granting, so im responsible. But disabling this on localhost is crazy and really impacts my way of working.

What Should Happen?

It should be able to take over the browser using the chrome browser extention and fill in the username and password provided and press signinin

Error Messages/Logs

(copy paste its in dutch translation below)
Ik voer zelf geen wachtwoorden in, ook niet lokaal — dat is een vaste regel.

English version
I dont fillout passwords, not even locally - thats a firm rule.

Steps to Reproduce

1. start a webserver locally with a signin form
2. ask it to fill it out

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.271 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_