TPM-backed HTTP message signatures

[getvictor]

For #28818

@noahtalerman @rachaelshaw We need to add a config setting on the server to block traffic for hosts without HTTP signatures. Some options are:

• server setting or env variable
• setting per team
• setting per enroll secret, like mark an enroll secret if it requires TPM

Question for customer:

We are allowing hosts with TPM-based host identity certs to coexist with hosts without certs (using the fleetd package without the new switch). We don't have a UI/API defined yet to let you see which hosts have a cert and which ones don't, but this can be done with a MySQL DB query. Are you OK with this audit info (knowing if a host has a cert after they enroll), or do you need us to block hosts from enrolling if they're trying to enroll without having a host identity cert?

Answer:

We want Fleet to require http message signatures. Hosts that don’t send a valid http message signature would have to re-enroll. I don’t understand if host identity certs is another step beyond that…

[lucasmrod]

Simplest for MVP IMO is "server setting or env variable".

[noahtalerman]

@getvictor makes sense to add a new server config! I think we just need to decide on naming / description. Up to y'all. Can you please open a PR against the reference docs release branch with the proposed new config? That way @rachaelshaw can review.

Also, what happens when you don’t have the flag set? Any host (whether or not they’re using the identity cert) can communicate with Fleet, right? If that's the case, I think we just want to make that clear in the reference docs.

[getvictor]

A server config that applies to all the hosts means that we can't dogfood this feature (since we have macOS, Windows, VMs without TPM, and ChromeOS). Also, customers can't try out this feature in their canary team, for example.

I like a more granular approach, such as a team-based option. If the team option is not set, we can default it to the global option, as we do for other options.

As currently coded, if a host requests a host identity cert, the Fleet server will expect all orbit/osquery traffic from that host to have an HTTP signature. So, HTTP signatures will be supported even if the above option is not set.

[noahtalerman]

customer-interkosmos is currently the only customer going to use this. They're deploying Fleet to only Linux workstations. I don't think they're going to do a granular "roll-out". They'll require it from the start.

Can we have the server config only apply to Linux hosts? This would let us dogfood.

We want to err on what’s simple for us because this feature is mission critical for the customer. Extra security isn't core to Fleet. Sounds like the server config is simplest for us.

More on "mission-critical" v. "core":

[getvictor]

Moving discussion back to Slack.