带有来自商店C＃.Net CNG的密钥的ECDSA签名文件

I'm trying to sign a file with ECDSA using the CNG API and a certificate from the Microsoft Certificate Store. I've read through a lot of documentation and and near done but I get hung up on importing the private key from the certificate. I've done this very same thing with RSA but it appears to be done very differently. Here's the code I have so far:I'm trying to sign a file with ECDSA using the