RFC2560 mandates that a valid OCSP response will contain exactly one
relevant certificate.  However, some OCSP responders include
extraneous certificates.  iPXE currently assumes that the first
certificate in the OCSP response is the relevant certificate; OCSP
checks will therefore fail if the responder includes the extraneous
certificates before the relevant certificate.

Fix by using the responder ID to identify the relevant certificate.

Reported-by: Christian Stroehmeier <stroemi@mail.uni-paderborn.de>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

iPXE has no concept of the local time zone, mainly because there is no
viable way to obtain time zone information in the absence of local
state.  This causes potential problems with newly-issued certificates
and certificates that are about to expire.

Avoid such problems by allowing an error margin of around 12 hours on
certificate validity periods, similar to the error margin already
allowed for OCSP response timestamps.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Add support for constructing OCSP queries and parsing OCSP responses.
(There is no support yet for actually issuing an OCSP query via an
HTTP POST.)

Signed-off-by: Michael Brown <mcb30@ipxe.org>