Response.headers does not include ETag

I’m using the fetch API to pull down assets from GitHub, and would like to use caching to avoid rate limiting issues at GH.

Ideally I would be able to use the ETag header, but it appears that the ETag does not make it through. Note that GitHub’s API requests that this be allowed:

< access-control-expose-headers: ETag, Link, Location, Retry-After, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Used, X-RateLimit-Resource, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval, X-GitHub-Media-Type, X-GitHub-SSO, X-GitHub-Request-Id, Deprecation, Sunset