Wire a custom error code for cert errors

This addesses UX's #1 concern about the UX flow for servers that require
certs - users don't know what to do after an error, so they want to kick
them into the certificate selection flow.

Bug: 5280071
Change-Id: I566707b9e680b3ef0b4c0cc8a07a8ad2c825ecaa
3 files changed