crypto/x509: rewrite the parser to use x/crypto/cryptobyte

[rolandshoemaker]

A x/crypto/cryptobyte parser has two advantages over an encoding/asn1 based parser: significant performance improvement due to avoiding reflection, and a much stricter profile/narrower security surface by only needing to support the X.509 profile rather than supporting all of the generic ASN.1 features.

https://go-review.googlesource.com/c/go/+/274234 contains a WIP rewrite which shows around 65% performance improvement and 70% reduction in memory allocations when parsing a typical web PKI certificate.

[rolandshoemaker]

Improving the performance of the parser could also address #35504, and if not exposing the cryptobyte based SAN parser to the tls package could also be a viable solution.

[gopherbot]

This issue is currently labeled as early-in-cycle for Go 1.17.
That time is now, so a friendly reminder to look at it again.

[ianlancetaylor]

Is this going to happen for 1.17? Thanks.

[neild]

This appears to have been completed in CL 274234.