x/crypto/ocsp: ParseResponse pitfalls

[takeyourhatoff]

There are two pitfalls in the ParseResponse method of "x/cryto/ocsp". The first being that if you forget to pass in an issuer then the response will be parsed but signature verification will not be performed. The second is that some people might assume that when err != nil, Response.Status == Good. I would suggest an additional idiot proof method VerifyResponse which might look a little like this:

https://play.golang.org/p/eTkpQi_gDk

[adg]

cc @agl

[odeke-em]

Hello there @takeyourhatoff, still interested in working on this? Perhaps a CL might re-ignite the conversation and it can then be reviewed. Thanks!