fix(settings): read PEM files but b64 env vars

- Extract base64 data from PEM files and secret files
- Environment variables are not PEM encoded and only the base64 data
- Affects OpenVPN certificate, key and encrypted key

internal/configuration/sources/files/helpers.go

@@ -1,9 +1,12 @@
 package files
 
 import (
+	"fmt"
 	"io"
 	"os"
 	"strings"
+
+	"github.com/qdm12/gluetun/internal/openvpn/extract"
 )
 
 // ReadFromFile reads the content of the file as a string.
@@ -32,3 +35,21 @@ func ReadFromFile(filepath string) (s *string, err error) {
 	content = strings.TrimSuffix(content, "\n")
 	return &content, nil
 }
+
+func readPEMFile(filepath string) (base64Ptr *string, err error) {
+	pemData, err := ReadFromFile(filepath)
+	if err != nil {
+		return nil, fmt.Errorf("reading file: %w", err)
+	}
+
+	if pemData == nil {
+		return nil, nil //nolint:nilnil
+	}
+
+	base64Data, err := extract.PEM([]byte(*pemData))
+	if err != nil {
+		return nil, fmt.Errorf("extracting base64 encoded data from PEM content: %w", err)
+	}
+
+	return &base64Data, nil
+}