Maint: internal/openvpn/parse package

- Parse PEM key data for Cyberghost and VPNUnlimited
- Add more unit tests

internal/openvpn/parse/pem.go

@@ -0,0 +1,27 @@
+package parse
+
+import (
+	"encoding/pem"
+	"errors"
+	"strings"
+)
+
+var (
+	errPEMDecode = errors.New("cannot decode PEM encoded block")
+)
+
+func extractPEM(b []byte, name string) (encodedData string, err error) {
+	name = strings.ToUpper(name) // certificate -> CERTIFICATE
+
+	pemBlock, _ := pem.Decode(b)
+	if pemBlock == nil {
+		return "", errPEMDecode
+	}
+
+	encodedBytes := pem.EncodeToMemory(pemBlock)
+	encodedData = string(encodedBytes)
+	encodedData = strings.ReplaceAll(encodedData, "\n", "")
+	encodedData = strings.TrimPrefix(encodedData, "-----BEGIN "+name+"-----")
+	encodedData = strings.TrimSuffix(encodedData, "-----END "+name+"-----")
+	return encodedData, nil
+}