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

### Preflight Checklist

- [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) 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

```shell
(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_