Motivation

http://Backend.AI ’s authentication signature depends on the Date HTTP header:

However, when using Webserver as a proxy, it is currently impossible to forward the client’s original Date header to the upstream server, because the Request.fetch() method always refreshes and overrides the Date header as part of its internal behavior:

• Proxy refresh logic:
  https://github.com/lablup/backend.ai/blob/f2afa387deea7bcb42d8f322ec4faf426f7ab626/src/ai/backend/web/proxy.py#L235
• Request behavior:
  https://github.com/lablup/backend.ai/blob/f2afa387deea7bcb42d8f322ec4faf426f7ab626/src/ai/backend/client/request.py#L320

This prevents implementations that rely on Date-header–based signature authentication from functioning correctly behind a proxy.

Required Features

Extend Request.fetch() to support explicit header overrides, so that the caller can force specific values (e.g., Date) to be used instead of the internally refreshed ones.

Example usage:

request.fetch(
    headers={
        "Date": "Tue, 02 Sep 2025 08:00:00 GMT",
    }
)

Impact

This would ensure that the provided Date header is preserved and passed through, enabling signature-based authentication behind proxies.

Testing Scenarios

JIRA Issue: BA-2257