AUTH-1557: Short Lived Certs

sshgen/sshgen.go

@@ -0,0 +1,163 @@
+package sshgen
+
+import (
+	"bytes"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/x509"
+	"encoding/json"
+	"encoding/pem"
+	"errors"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/cloudflare/cloudflared/cmd/cloudflared/config"
+	cfpath "github.com/cloudflare/cloudflared/cmd/cloudflared/path"
+	"github.com/coreos/go-oidc/jose"
+	homedir "github.com/mitchellh/go-homedir"
+	gossh "golang.org/x/crypto/ssh"
+)
+
+const (
+	signEndpoint = "/cdn-cgi/access/cert_sign"
+	keyName      = "cf_key"
+)
+
+// signPayload represents the request body sent to the sign handler API
+type signPayload struct {
+	PublicKey string `json:"public_key"`
+	JWT       string `json:"jwt"`
+	Issuer    string `json:"issuer"`
+}
+
+// signResponse represents the response body from the sign handler API
+type signResponse struct {
+	KeyID       string    `json:"id"`
+	Certificate string    `json:"certificate"`
+	ExpiresAt   time.Time `json:"expires_at"`
+}
+
+// GenerateShortLivedCertificate generates and stores a keypair for short lived certs
+func GenerateShortLivedCertificate(appURL *url.URL, token string) error {
+	fullName, err := cfpath.GenerateFilePathFromURL(appURL, keyName)
+	if err != nil {
+		return err
+	}
+
+	cert, err := handleCertificateGeneration(token, fullName)
+	if err != nil {
+		return err
+	}
+
+	name := fullName + "-cert.pub"
+	if err := writeKey(name, []byte(cert)); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// handleCertificateGeneration takes a JWT and uses it build a signPayload
+// to send to the Sign endpoint with the public key from the keypair it generated
+func handleCertificateGeneration(token, fullName string) (string, error) {
+	if token == "" {
+		return "", errors.New("invalid token")
+	}
+
+	jwt, err := jose.ParseJWT(token)
+	if err != nil {
+		return "", err
+	}
+
+	claims, err := jwt.Claims()
+	if err != nil {
+		return "", err
+	}
+
+	issuer, _, err := claims.StringClaim("iss")
+	if err != nil {
+		return "", err
+	}
+
+	pub, err := generateKeyPair(fullName)
+	if err != nil {
+		return "", err
+	}
+
+	buf, err := json.Marshal(&signPayload{
+		PublicKey: string(pub),
+		JWT:       token,
+		Issuer:    issuer,
+	})
+	if err != nil {
+		return "", err
+	}
+
+	res, err := http.Post(issuer+signEndpoint, "application/json", bytes.NewBuffer(buf))
+	if err != nil {
+		return "", err
+	}
+	defer res.Body.Close()
+
+	decoder := json.NewDecoder(res.Body)
+	var signRes signResponse
+	if err := decoder.Decode(&signRes); err != nil {
+		return "", err
+	}
+	return signRes.Certificate, err
+}
+
+// generateKeyPair creates a EC keypair (P256) and stores them in the homedir.
+// returns the generated public key from the successful keypair generation
+func generateKeyPair(fullName string) ([]byte, error) {
+	pubKeyName := fullName + ".pub"
+
+	exist, err := config.FileExists(pubKeyName)
+	if err != nil {
+		return nil, err
+	}
+	if exist {
+		return ioutil.ReadFile(pubKeyName)
+	}
+
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return nil, err
+	}
+	parsed, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return nil, err
+	}
+
+	if err := writeKey(fullName, pem.EncodeToMemory(&pem.Block{
+		Type:  "EC PRIVATE KEY",
+		Bytes: parsed,
+	})); err != nil {
+		return nil, err
+	}
+
+	pub, err := gossh.NewPublicKey(&key.PublicKey)
+	if err != nil {
+		return nil, err
+	}
+	data := gossh.MarshalAuthorizedKey(pub)
+
+	if err := writeKey(pubKeyName, data); err != nil {
+		return nil, err
+	}
+
+	return data, nil
+}
+
+// writeKey will write a key to disk in DER format (it's a standard pem key)
+func writeKey(filename string, data []byte) error {
+	filepath, err := homedir.Expand(filename)
+	if err != nil {
+		return err
+	}
+
+	return ioutil.WriteFile(filepath, data, 0600)
+}