如何使用Go Golang签署文件

If I generate my key with openssl like this:

openssl req -x509 -sha256 -nodes -days 365 -newkey rsa:2048 -keyout testsign.key -out testsign.crt

What Go or Golang library or method or tool can I use to sign a file with that key?

To satisfy the requirements I needed to accomplish with Go & OpenSSL, it's as straight forward as executing command line:

    c := "openssl"
    a := []string{"dgst", "-sha512", "-sign", "signature.key", "-out", "FileOut.signed", "FileToBeSigned.txt"}   
    cmd := exec.Command(c, a...)