CryptAcquireCertificatePrivateKey

[DllImport("Crypt32.dll", SetLastError = true)]
public static extern bool CryptAcquireCertificatePrivateKey(
   IntPtr pCert,
   uint dwFlags,
   IntPtr pvReserved,
   ref IntPtr phCryptProv,
   ref uint pdwKeySpec,
   ref bool pfCallerFreeProv
);

Microsoft documentation: Link