AUTH-2018: Adds support for authorized keys and short lived certs

sshserver/authentication.go

@@ -0,0 +1,97 @@
+//+build !windows
+
+package sshserver
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+
+	"github.com/gliderlabs/ssh"
+	"github.com/pkg/errors"
+	gossh "golang.org/x/crypto/ssh"
+)
+
+var (
+	systemConfigPath  = "/etc/cloudflared/"
+	authorizeKeysPath = ".cloudflared/authorized_keys"
+)
+
+func (s *SSHServer) authorizedKeyHandler(ctx ssh.Context, key ssh.PublicKey) bool {
+	sshUser, err := s.getUserFunc(ctx.User())
+	if err != nil {
+		s.logger.Debugf("Invalid user: %s", ctx.User())
+		return false
+	}
+
+	authorizedKeysPath := path.Join(sshUser.HomeDir, authorizeKeysPath)
+	if _, err := os.Stat(authorizedKeysPath); os.IsNotExist(err) {
+		s.logger.Debugf("authorized_keys file %s not found", authorizeKeysPath)
+		return false
+	}
+
+	authorizedKeysBytes, err := ioutil.ReadFile(authorizedKeysPath)
+	if err != nil {
+		s.logger.WithError(err).Errorf("Failed to load authorized_keys %s", authorizedKeysPath)
+		return false
+	}
+
+	for len(authorizedKeysBytes) > 0 {
+		// Skips invalid keys. Returns error if no valid keys remain.
+		pubKey, _, _, rest, err := ssh.ParseAuthorizedKey(authorizedKeysBytes)
+		authorizedKeysBytes = rest
+		if err != nil {
+			s.logger.WithError(err).Errorf("No valid keys found in %s", authorizeKeysPath)
+			return false
+		}
+
+		if ssh.KeysEqual(pubKey, key) {
+			ctx.SetValue("sshUser", sshUser)
+			return true
+		}
+	}
+	s.logger.Debugf("Matching public key not found in %s", authorizeKeysPath)
+	return false
+}
+
+func (s *SSHServer) shortLivedCertHandler(ctx ssh.Context, key ssh.PublicKey) bool {
+	userCert, ok := key.(*gossh.Certificate)
+	if !ok {
+		s.logger.Debug("Received key is not an SSH certificate")
+		return false
+	}
+
+	if !ssh.KeysEqual(s.caCert, userCert.SignatureKey) {
+		s.logger.Debug("CA certificate does not match user certificate signer")
+		return false
+	}
+
+	checker := gossh.CertChecker{}
+	if err := checker.CheckCert(ctx.User(), userCert); err != nil {
+		s.logger.Debug(err)
+		return false
+	} else {
+		sshUser, err := s.getUserFunc(ctx.User())
+		if err != nil {
+			s.logger.Debugf("Invalid user: %s", ctx.User())
+			return false
+		}
+		ctx.SetValue("sshUser", sshUser)
+	}
+	return true
+}
+
+func getCACert() (ssh.PublicKey, error) {
+	caCertPath := path.Join(systemConfigPath, "ca.pub")
+	caCertBytes, err := ioutil.ReadFile(caCertPath)
+	if err != nil {
+		return nil, errors.Wrap(err, fmt.Sprintf("Failed to load CA certertificate %s", caCertPath))
+	}
+	caCert, _, _, _, err := ssh.ParseAuthorizedKey(caCertBytes)
+	if err != nil {
+		return nil, errors.Wrap(err, "Failed to parse CA Certificate")
+	}
+
+	return caCert, nil
+}