Improve Mac OS Certificate Parsing to import PEM directly

[gfs]

The PEM exported by the Mac OS Keychain is all of the certificates base64 encoded and then stitched together with --- BEGIN CERTIFICATE --- and --- END CERTIFICATE --- blocks. After .NET 5 its possible to load a certificate from base64 encoded text with X509Certificate2.CreateFromPem

https://docs.microsoft.com/en-us/dotnet/api/system.security.cryptography.x509certificates.x509certificate2.createfrompem?view=net-6.0

Proposed solution:

1. Use existing security call to generate PEM.
2. The result is already stored in a string - instead of writing out to a file, just split that string into chunks of base64 data, stripping out the headers.
3. With each chunk call X509Certificate2.CreateFromPem
4. Report the certificate

Code point to modify:

AttackSurfaceAnalyzer/Lib/Collectors/CertificateCollector.cs

Line 104 in 6cc160f

if (ExternalCommandRunner.RunExternalCommand("openssl", $"pkcs12 -export -nokeys -out {pkPath} -passout pass:pass -in {tmpPath}", out string _, out string _) == 0)