chore: update vendor

vendor/github.com/google/certificate-transparency-go/x509util/files.go

@@ -19,7 +19,10 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"net/url"
 	"strings"
+
+	"github.com/google/certificate-transparency-go/x509"
 )
 
 // ReadPossiblePEMFile loads data from a file which may be in DER format
@@ -71,3 +74,42 @@ func dePEM(data []byte, blockname string) [][]byte {
 	}
 	return results
 }
+
+// ReadFileOrURL returns the data from a target which may be either a filename
+// or an HTTP(S) URL.
+func ReadFileOrURL(target string, client *http.Client) ([]byte, error) {
+	u, err := url.Parse(target)
+	if err != nil || (u.Scheme != "http" && u.Scheme != "https") {
+		return ioutil.ReadFile(target)
+	}
+
+	rsp, err := client.Get(u.String())
+	if err != nil {
+		return nil, fmt.Errorf("failed to http.Get(%q): %v", target, err)
+	}
+	return ioutil.ReadAll(rsp.Body)
+}
+
+// GetIssuer attempts to retrieve the issuer for a certificate, by examining
+// the cert's Authority Information Access extension (if present) for the
+// issuer's URL and retrieving from there.
+func GetIssuer(cert *x509.Certificate, client *http.Client) (*x509.Certificate, error) {
+	if len(cert.IssuingCertificateURL) == 0 {
+		return nil, nil
+	}
+	issuerURL := cert.IssuingCertificateURL[0]
+	rsp, err := client.Get(issuerURL)
+	if err != nil || rsp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("failed to get issuer from %q: %v", issuerURL, err)
+	}
+	defer rsp.Body.Close()
+	body, err := ioutil.ReadAll(rsp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read issuer from %q: %v", issuerURL, err)
+	}
+	issuers, err := x509.ParseCertificates(body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse issuer cert: %v", err)
+	}
+	return issuers[0], nil
+}