(Go) Duplicate openssl dgst -sha256 -sign private.pem -out sha256.sig in.dat

Demonstrates how to duplicate this OpenSSL command:

openssl dgst -sha256 -sign private.pem -out sha256.sig in.dat

1. Creates a SHA256 digest of the contents of the input file
2. Signs the SHA256 digest using the private key.

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    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    pkey := chilkat.NewPrivateKey()

    // Load the private key from an PEM file:
    success := pkey.LoadPemFile("private.pem")
    if success != true {
        fmt.Println(pkey.LastErrorText())
        pkey.DisposePrivateKey()
        return
    }

    rsa := chilkat.NewRsa()

    // Import the private key into the RSA component:
    success = rsa.ImportPrivateKeyObj(pkey)
    if success != true {
        fmt.Println(rsa.LastErrorText())
        pkey.DisposePrivateKey()
        rsa.DisposeRsa()
        return
    }

    // OpenSSL uses big-endian.
    rsa.SetLittleEndian(false)

    // Load the file to be signed.
    bdFileData := chilkat.NewBinData()
    success = bdFileData.LoadFile("in.dat")

    bdSig := chilkat.NewBinData()
    success = rsa.SignBd(bdFileData,"sha256",bdSig)
    if success != true {
        fmt.Println(rsa.LastErrorText())
        pkey.DisposePrivateKey()
        rsa.DisposeRsa()
        bdFileData.DisposeBinData()
        bdSig.DisposeBinData()
        return
    }

    // Save the binary signature to a file.
    success = bdSig.WriteFile("signature.sig")
    if success != true {
        fmt.Println("Failed to write signature.sig.")
        pkey.DisposePrivateKey()
        rsa.DisposeRsa()
        bdFileData.DisposeBinData()
        bdSig.DisposeBinData()
        return
    }

    fmt.Println("Success.")

    pkey.DisposePrivateKey()
    rsa.DisposeRsa()
    bdFileData.DisposeBinData()
    bdSig.DisposeBinData()