add support for .pem cert format

Author: umbynos

docs/usage.md

@@ -74,7 +74,7 @@ The tool offers also the ability to flash SSL certificates to a module:
 ./arduino-fwuploader certificates flash -b arduino:samd:nano_33_iot" -a COM10 -u arduino.cc:443 -u google.com:443
 ```
 
-or you can specify a path to a file in `.der` format with `-f` instead of the URL of the certificate
+or you can specify a path to a file in `.der` format or in `.pem` format with `-f` or `--file` instead of the URL of the certificate
 
 Due to a limitation on the handling of certs in the NINA modules, when `certificates flash` command is launched, all the
 previous certificates are going to be erased. To overcome this it's required to upload them all together:

flasher/nina.go

@@ -147,14 +147,21 @@ func (f *NinaFlasher) certificateFromFile(certificateFile *paths.Path) ([]byte,
 		logrus.Error(err)
 		return nil, err
 	}
-
-	cert, err := x509.ParseCertificate(data)
-	if err != nil {
-		logrus.Error(err)
-		return nil, err
+	switch certificateFile.Ext() {
+	case ".cer":
+		// the data needs to be formatted in PEM format
+		cert, err := x509.ParseCertificate(data)
+		if err != nil {
+			logrus.Error(err)
+			return nil, err
+		}
+		return pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: cert.Raw}), nil
+	case ".pem":
+		// the data is already encoded in pem format and we do not need to parse it.
+		return data, nil
+	default:
+		return nil, fmt.Errorf("cert format %s not supported, please use .pem or .cer", certificateFile.Ext())
 	}
-
-	return pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: cert.Raw}), nil
 }
 
 func (f *NinaFlasher) certificateFromURL(URL string) ([]byte, error) {

flasher/winc.go

@@ -119,14 +119,20 @@ func (f *WincFlasher) certificateFromFile(certificateFile *paths.Path) ([]byte,
 		logrus.Error(err)
 		return nil, err
 	}
-
-	cert, err := x509.ParseCertificate(data)
-	if err != nil {
-		logrus.Error(err)
-		return nil, err
+	switch certificateFile.Ext() {
+	case ".cer":
+		cert, err := x509.ParseCertificate(data)
+		if err != nil {
+			logrus.Error(err)
+			return nil, err
+		}
+		return f.getCertificateData(cert)
+	case ".pem":
+		// the data is already encoded in pem format and we do not need to parse it.
+		return data, nil
+	default:
+		return nil, fmt.Errorf("cert format %s not supported, please use .pem or .cer", certificateFile.Ext())
 	}
-
-	return f.getCertificateData(cert)
 }
 
 func (f *WincFlasher) certificateFromURL(URL string) ([]byte, error) {