x509: certificate signed by unknown authority

I'm getting this error on the Mac client:

`ERROR CODE 1601 - API network error: doRetry failed, at tempts: 3, timeout 5.324s, last err: Get "https://api-0.core.keybaseapi.com/_/api/1.0/home.json?num_people=10O&record_visit=0": x509: certificate signed by unknown authority in method keybase. 1.home. homeGetScreen`

I tried manually trusting the cert for `api-0.core.keybaseapi.com` in my keychain, but that didn't help. And since the client can't use the API, I was unable to submit feedback or logs there.

Reproduce the certificate error on the Mac client and trace the request to api-0.core.keybaseapi.com. No source files or tests are named in the issue, so first locate the client’s TLS/API networking entry point and determine why the certificate is rejected. Done means the client can reach the API without manually trusting the certificate, with a regression check if the relevant test area is found.

Written by the indexing model from the issue text.