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tls_auth.go
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tls_auth.go
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package v1
import (
"bytes"
"crypto"
"crypto/x509"
"encoding/pem"
"fmt"
"io"
"net/http"
"net/url"
"os"
"time"
"github.com/gin-gonic/gin"
log "github.com/sirupsen/logrus"
"golang.org/x/crypto/ocsp"
)
type TLSAuth struct {
AllowedOUs []string
CrlPath string
revocationCache map[string]cacheEntry
cacheExpiration time.Duration
logger *log.Entry
}
type cacheEntry struct {
revoked bool
timestamp time.Time
}
func (ta *TLSAuth) ocspQuery(server string, cert *x509.Certificate, issuer *x509.Certificate) (*ocsp.Response, error) {
req, err := ocsp.CreateRequest(cert, issuer, &ocsp.RequestOptions{Hash: crypto.SHA256})
if err != nil {
ta.logger.Errorf("TLSAuth: error creating OCSP request: %s", err)
return nil, err
}
httpRequest, err := http.NewRequest(http.MethodPost, server, bytes.NewBuffer(req))
if err != nil {
ta.logger.Error("TLSAuth: cannot create HTTP request for OCSP")
return nil, err
}
ocspURL, err := url.Parse(server)
if err != nil {
ta.logger.Error("TLSAuth: cannot parse OCSP URL")
return nil, err
}
httpRequest.Header.Add("Content-Type", "application/ocsp-request")
httpRequest.Header.Add("Accept", "application/ocsp-response")
httpRequest.Header.Add("host", ocspURL.Host)
httpClient := &http.Client{}
httpResponse, err := httpClient.Do(httpRequest)
if err != nil {
ta.logger.Error("TLSAuth: cannot send HTTP request to OCSP")
return nil, err
}
defer httpResponse.Body.Close()
output, err := io.ReadAll(httpResponse.Body)
if err != nil {
ta.logger.Error("TLSAuth: cannot read HTTP response from OCSP")
return nil, err
}
ocspResponse, err := ocsp.ParseResponseForCert(output, cert, issuer)
return ocspResponse, err
}
func (ta *TLSAuth) isExpired(cert *x509.Certificate) bool {
now := time.Now().UTC()
if cert.NotAfter.UTC().Before(now) {
ta.logger.Errorf("TLSAuth: client certificate is expired (NotAfter: %s)", cert.NotAfter.UTC())
return true
}
if cert.NotBefore.UTC().After(now) {
ta.logger.Errorf("TLSAuth: client certificate is not yet valid (NotBefore: %s)", cert.NotBefore.UTC())
return true
}
return false
}
// isOCSPRevoked checks if the client certificate is revoked by any of the OCSP servers present in the certificate.
// It returns a boolean indicating if the certificate is revoked and a boolean indicating if the OCSP check was successful and could be cached.
func (ta *TLSAuth) isOCSPRevoked(cert *x509.Certificate, issuer *x509.Certificate) (bool, bool) {
if cert.OCSPServer == nil || len(cert.OCSPServer) == 0 {
ta.logger.Infof("TLSAuth: no OCSP Server present in client certificate, skipping OCSP verification")
return false, true
}
for _, server := range cert.OCSPServer {
ocspResponse, err := ta.ocspQuery(server, cert, issuer)
if err != nil {
ta.logger.Errorf("TLSAuth: error querying OCSP server %s: %s", server, err)
continue
}
switch ocspResponse.Status {
case ocsp.Good:
return false, true
case ocsp.Revoked:
ta.logger.Errorf("TLSAuth: client certificate is revoked by server %s", server)
return true, true
case ocsp.Unknown:
log.Debugf("unknow OCSP status for server %s", server)
continue
}
}
log.Infof("Could not get any valid OCSP response, assuming the cert is revoked")
return true, false
}
// isCRLRevoked checks if the client certificate is revoked by the CRL present in the CrlPath.
// It returns a boolean indicating if the certificate is revoked and a boolean indicating if the CRL check was successful and could be cached.
func (ta *TLSAuth) isCRLRevoked(cert *x509.Certificate) (bool, bool) {
if ta.CrlPath == "" {
ta.logger.Info("no crl_path, skipping CRL check")
return false, true
}
crlContent, err := os.ReadFile(ta.CrlPath)
if err != nil {
ta.logger.Errorf("could not read CRL file, skipping check: %s", err)
return false, false
}
crlBinary, rest := pem.Decode(crlContent)
if len(rest) > 0 {
ta.logger.Warn("CRL file contains more than one PEM block, ignoring the rest")
}
crl, err := x509.ParseRevocationList(crlBinary.Bytes)
if err != nil {
ta.logger.Errorf("could not parse CRL file, skipping check: %s", err)
return false, false
}
now := time.Now().UTC()
if now.After(crl.NextUpdate) {
ta.logger.Warn("CRL has expired, will still validate the cert against it.")
}
if now.Before(crl.ThisUpdate) {
ta.logger.Warn("CRL is not yet valid, will still validate the cert against it.")
}
for _, revoked := range crl.RevokedCertificateEntries {
if revoked.SerialNumber.Cmp(cert.SerialNumber) == 0 {
ta.logger.Warn("client certificate is revoked by CRL")
return true, true
}
}
return false, true
}
func (ta *TLSAuth) isRevoked(cert *x509.Certificate, issuer *x509.Certificate) (bool, error) {
sn := cert.SerialNumber.String()
if cacheValue, ok := ta.revocationCache[sn]; ok {
if time.Now().UTC().Sub(cacheValue.timestamp) < ta.cacheExpiration {
ta.logger.Debugf("TLSAuth: using cached value for cert %s: %t", sn, cacheValue.revoked)
return cacheValue.revoked, nil
}
ta.logger.Debugf("TLSAuth: cached value expired, removing from cache")
delete(ta.revocationCache, sn)
} else {
ta.logger.Tracef("TLSAuth: no cached value for cert %s", sn)
}
revokedByOCSP, cacheOCSP := ta.isOCSPRevoked(cert, issuer)
revokedByCRL, cacheCRL := ta.isCRLRevoked(cert)
revoked := revokedByOCSP || revokedByCRL
if cacheOCSP && cacheCRL {
ta.revocationCache[sn] = cacheEntry{
revoked: revoked,
timestamp: time.Now().UTC(),
}
}
return revoked, nil
}
func (ta *TLSAuth) isInvalid(cert *x509.Certificate, issuer *x509.Certificate) (bool, error) {
if ta.isExpired(cert) {
return true, nil
}
revoked, err := ta.isRevoked(cert, issuer)
if err != nil {
//Fail securely, if we can't check the revocation status, let's consider the cert invalid
//We may change this in the future based on users feedback, but this seems the most sensible thing to do
return true, fmt.Errorf("could not check for client certification revocation status: %w", err)
}
return revoked, nil
}
func (ta *TLSAuth) SetAllowedOu(allowedOus []string) error {
for _, ou := range allowedOus {
//disallow empty ou
if ou == "" {
return fmt.Errorf("empty ou isn't allowed")
}
//drop & warn on duplicate ou
ok := true
for _, validOu := range ta.AllowedOUs {
if validOu == ou {
ta.logger.Warningf("dropping duplicate ou %s", ou)
ok = false
}
}
if ok {
ta.AllowedOUs = append(ta.AllowedOUs, ou)
}
}
return nil
}
func (ta *TLSAuth) ValidateCert(c *gin.Context) (bool, string, error) {
//Checks cert validity, Returns true + CN if client cert matches requested OU
var clientCert *x509.Certificate
if c.Request.TLS == nil || len(c.Request.TLS.PeerCertificates) == 0 {
//do not error if it's not TLS or there are no peer certs
return false, "", nil
}
if len(c.Request.TLS.VerifiedChains) > 0 {
validOU := false
clientCert = c.Request.TLS.VerifiedChains[0][0]
for _, ou := range clientCert.Subject.OrganizationalUnit {
for _, allowedOu := range ta.AllowedOUs {
if allowedOu == ou {
validOU = true
break
}
}
}
if !validOU {
return false, "", fmt.Errorf("client certificate OU (%v) doesn't match expected OU (%v)",
clientCert.Subject.OrganizationalUnit, ta.AllowedOUs)
}
revoked, err := ta.isInvalid(clientCert, c.Request.TLS.VerifiedChains[0][1])
if err != nil {
ta.logger.Errorf("TLSAuth: error checking if client certificate is revoked: %s", err)
return false, "", fmt.Errorf("could not check for client certification revocation status: %w", err)
}
if revoked {
return false, "", fmt.Errorf("client certificate for CN=%s OU=%s is revoked", clientCert.Subject.CommonName, clientCert.Subject.OrganizationalUnit)
}
ta.logger.Debugf("client OU %v is allowed vs required OU %v", clientCert.Subject.OrganizationalUnit, ta.AllowedOUs)
return true, clientCert.Subject.CommonName, nil
}
return false, "", fmt.Errorf("no verified cert in request")
}
func NewTLSAuth(allowedOus []string, crlPath string, cacheExpiration time.Duration, logger *log.Entry) (*TLSAuth, error) {
ta := &TLSAuth{
revocationCache: map[string]cacheEntry{},
cacheExpiration: cacheExpiration,
CrlPath: crlPath,
logger: logger,
}
err := ta.SetAllowedOu(allowedOus)
if err != nil {
return nil, err
}
return ta, nil
}