Web and desktop clients cannot authenticate with Unicode server credentials

Description

The web and desktop clients pass username:password directly to btoa() when creating a Basic-auth token. btoa() accepts only binary strings, so credentials containing characters outside the one-byte range throw InvalidCharacterError. Characters such as ä do not throw, but are encoded as a single byte instead of UTF-8, so the server decodes a different password and rejects authentication.

This affects server health checks, protocol detection, API clients, and legacy terminal authentication because they share the same credential encoder. The server already generates and decodes Basic-auth credentials as UTF-8. The app should convert the credential string to UTF-8 bytes before applying standard Base64 encoding.

Plugins

N/A

OpenCode version

N/A (reproduced in the shared client authentication helper)

Steps to reproduce

1. Start an OpenCode server with OPENCODE_SERVER_PASSWORD='秘密🔐'.
2. Open the web or desktop client and add that server.
3. Enter the same password and attempt to connect.
4. Observe that encoding throws InvalidCharacterError and the connection cannot be established.

A second case is päss: encoding does not throw, but the server receives invalid UTF-8 and authentication fails.

Expected behavior: Unicode usernames and passwords should be encoded as UTF-8 bytes before Base64 encoding and should authenticate successfully.

Screenshot and/or share link

Not provided; the credential helper provides a deterministic reproduction.

Operating System

All

Terminal

Web and desktop clients