[Ohai] Proxy<>Target signals

[Christopher Wood <[e-mail]>]

Hi folks,

One of the topics discussed during our meeting at IETF 113 was whether the proxy could attach client metadata to requests to the target (to use the ODoH terminology). A shadow ban bit was the primary example, initially raised in issue #66. Issue #100 also raised the possibility of other metadata, like the client geo. Based on discussion during the meeting and the corresponding issues, we have an initial PR that explains the circumstances in which this type of data can be attached to forwarded requests by a proxy:

   https://github.com/ietf-wg-ohai/oblivious-http/pull/113

Please have a look and provide feedback. We’ll merge this soon barring objections.

Related to this topic is issue #114, which considers the relation between signals sent between proxy and target. As we consider target->proxy signals like rate limits, I think we ought to consider how this might be abused to narrow the client anonymity set in surprising ways. My current thinking is that a proxy must treat client requests independently of whatever signals it receives from a target since, if this is not done, requests the target sees may be correlated to past requests. I’d appreciate if folks would take a look at that issue and chime in ahead of 114. I’d like to discuss the issue then.

Thanks,
Chris