Support for PKCS#8 encoded RSA private keys in Windows port

[massi-ang]

Windows port only support RSA private keys in PKCS#1 format.
On Linux and MacOS, PKCS#8 private keys are supported

See also #259

[JonathanHenson]

pkcs 7 should also be supported. Looking into pkcs 8 at the moment

[JonathanHenson]

probably something like this is needed:
https://docs.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-cryptimportpkcs8

[massi-ang]

My suggestion would be to look at the first line of the PEM file to determine the format of the PEM: PKCS#1, PKCS#8 or SEC1 and then have different code branches to load the key.
I used this code to decode PKCS#8: https://github.com/odzhan/rsa/blob/63838b8799143c91b117d0785ef58c9ddbd3e436/rsa.c#L390

[MikeDombo]

+1, particularly for EC keys in PKCS#8 format.

The previously linked Microsoft API has been removed and this is now recommended: https://learn.microsoft.com/en-us/windows/win32/api/wincrypt/nf-wincrypt-pfximportcertstore

[jcosentino11]

I think this is also an issue on mac, was seeing static: failed to import certificate and private key with error 0. error, but that went away after converting the key to pkcs#1.