std.crypto.Certificate.verify: additionally verify "key usage"

[andrewrk]

RFC 5280 section 4.2.1.3

zig/lib/std/crypto/Certificate.zig

Lines 197 to 201 in c9ef277

	/// This function verifies:
	/// * That the subject's issuer is indeed the provided issuer.
	/// * The time validity of the subject.
	/// * The signature.
	pub fn verify(parsed_subject: Parsed, parsed_issuer: Parsed, now_sec: i64) VerifyError!void {

[clickingbuttons]

Not only should key usage be verified, but also:

• Additional key usage
• Policy chain
• Basic constraints
• All critical extensions are parsed
• Correctly parse dates before 1950 (currently they are all parsed as 1970)