Scrape all possible root certificate

In the uno r4 we're using mbedtls which has a strange behaviour. And some root certificates won't work. Therfore the most simple solution is using all the possible ones, found during the handshake.

certificates/certutils.go

@@ -30,7 +30,7 @@ import (
 
 // ScrapeRootCertificatesFromURL downloads from a webserver the root certificate
 // required to connect to that server from the TLS handshake response.
-func ScrapeRootCertificatesFromURL(URL string) (*x509.Certificate, error) {
+func ScrapeRootCertificatesFromURL(URL string) ([]*x509.Certificate, error) {
 	conn, err := tls.Dial("tcp", URL, &tls.Config{
 		InsecureSkipVerify: false,
 	})
@@ -49,11 +49,12 @@ func ScrapeRootCertificatesFromURL(URL string) (*x509.Certificate, error) {
 	if len(chains) == 0 {
 		return nil, fmt.Errorf("no certificates found at %s", URL)
 	}
-	rootCertificate := chains[len(chains)-1]
-	if len(rootCertificate) == 0 {
-		return nil, fmt.Errorf("no certificates found at %s", URL)
+	rootCertificates := make([]*x509.Certificate, len(chains))
+	for i, chain := range chains {
+		// The last certificate of the chain is always the Root Certificate
+		rootCertificates[i] = chain[len(chain)-1]
 	}
-	return rootCertificate[len(rootCertificate)-1], nil
+	return rootCertificates, nil
 }
 
 // LoadCertificatesFromFile read certificates from the given file. PEM and CER formats

certificates/certutils_test.go

@@ -8,7 +8,9 @@ import (
 )
 
 func TestScrapeRootCertificatesFromURL(t *testing.T) {
-	cert, err := certificates.ScrapeRootCertificatesFromURL("www.arduino.cc:443")
+	rootCerts, err := certificates.ScrapeRootCertificatesFromURL("www.arduino.cc:443")
 	require.NoError(t, err)
-	require.Equal(t, cert.Issuer, cert.Subject)
+	for _, cert := range rootCerts {
+		require.Equal(t, cert.Issuer, cert.Subject)
+	}
 }

cli/certificates/flash.go

@@ -121,11 +121,11 @@ func flashCertificates(uploader *plugin.FwUploader, certificateURLs, certificate
 	for _, URL := range certificateURLs {
 		logrus.Infof("Converting and flashing certificate from %s", URL)
 		stdout.Write([]byte(fmt.Sprintf("Converting and flashing certificate from %s\n", URL)))
-		rootCert, err := certificates.ScrapeRootCertificatesFromURL(URL)
+		rootCerts, err := certificates.ScrapeRootCertificatesFromURL(URL)
 		if err != nil {
 			return nil, err
 		}
-		allCerts = append(allCerts, rootCert)
+		allCerts = append(allCerts, rootCerts...)
 	}
 
 	f, err := certsBundle.Create()