Feature Request: Allow tiktoken to accept a custom HTTP client

Summary

I’d like to request a feature that allows passing a custom HTTP client instance to tiktoken, rather than relying on the internal default client.

Motivation

In some environments, it’s necessary to use a custom HTTP client — for example, when the system must connect through a proxy or use a specific SSL certificate for verification. Currently, tiktoken doesn’t expose a way to inject a pre-configured client.

Example use case:

import httpx

custom_client = httpx.Client(verify="/path/to/custom/cert.pem")

tiktoken.encoding_for_model("gpt-4", http_client=custom_client)

Start by locating encoding_for_model and the current HTTP client setup, then inspect any tests covering encoding downloads. The work is done when callers can provide a custom client for proxy or certificate configuration while the existing default behavior remains available.