[Bug Fix] Added support for compound octet string

[nisargap]

Compound octet strings currently are not covered by the PKCS7 parsing function. For cases such as Apple Attest Validation or MS Crypto API this library can't be used until this is fixed.

See the original PR Patch (it was never merged in) : fullsailor#36

[nisargap]

cc for approval @g-k

[g-k]

Thanks for the PR! This seems reasonable.

Can you add some tests with fixtures from the Apple Attest Validation or MS Crypto API that exercises the new code? They can go in https://github.com/mozilla-services/pkcs7/blob/master/verify_test.go

[nisargap]

@g-k Just added a test with a sample apple attestation receipt fixture, with the new changes the full compound octet string content is able to be parsed by the parseSignedData function, with the old code it truncates the content

[nisargap]

cc: @g-k

[nisargap]

cc: @g-k can someone with write access merge? i've been maintaining my own fork for several weeks now, thank you!

[g-k]

I don't worked at Mozilla anymore, so I can't land any PRs.

Can't promise anything, but maybe @ajvb can take a look.

[nisargap]

cc for approval @ajvb