1 files changed, 83 insertions, 9 deletions

diff --git a/auth/token.go b/auth/token.go
index fc13c5bee..e1c196615 100644
--- a/auth/token.go
+++ b/auth/token.go
@@ -1,8 +1,14 @@
 package gitalyauth
 
 import (
+	"crypto/hmac"
+	"crypto/sha256"
 	"crypto/subtle"
 	"encoding/base64"
+	"encoding/hex"
+	"strconv"
+	"strings"
+	"time"
 
 	"github.com/grpc-ecosystem/go-grpc-middleware/auth"
 	"golang.org/x/net/context"
@@ -10,36 +16,104 @@ import (
 	"google.golang.org/grpc/status"
 )
 
+const (
+	timestampThreshold = 30 * time.Second
+)
+
 var (
 	errUnauthenticated = status.Errorf(codes.Unauthenticated, "authentication required")
 	errDenied          = status.Errorf(codes.PermissionDenied, "permission denied")
 )
 
+// AuthInfo contains the authentication information coming from a request
+type AuthInfo struct {
+	Version       string
+	SignedMessage []byte
+	Message       string
+}
+
 // CheckToken checks the 'authentication' header of incoming gRPC
 // metadata in ctx. It returns nil if and only if the token matches
 // secret.
-func CheckToken(ctx context.Context, secret string) error {
+func CheckToken(ctx context.Context, secret string, targetTime time.Time) error {
 	if len(secret) == 0 {
 		panic("CheckToken: secret may not be empty")
 	}
 
-	encodedToken, err := grpc_auth.AuthFromMD(ctx, "bearer")
+	authInfo, err := ExtractAuthInfo(ctx)
 	if err != nil {
 		return errUnauthenticated
 	}
 
-	token, err := base64.StdEncoding.DecodeString(encodedToken)
-	if err != nil {
-		return errUnauthenticated
-	}
+	switch authInfo.Version {
+	case "v1":
+		decodedToken, err := base64.StdEncoding.DecodeString(authInfo.Message)
+		if err != nil {
+			return errUnauthenticated
+		}
 
-	if !tokensEqual(token, []byte(secret)) {
-		return errDenied
+		if tokensEqual(decodedToken, []byte(secret)) {
+			return nil
+		}
+	case "v2":
+		if hmacInfoValid(authInfo.Message, authInfo.SignedMessage, []byte(secret), targetTime, timestampThreshold) {
+			return nil
+		}
 	}
 
-	return nil
+	return errDenied
 }
 
 func tokensEqual(tok1, tok2 []byte) bool {
 	return subtle.ConstantTimeCompare(tok1, tok2) == 1
 }
+
+// ExtractAuthInfo returns an `AuthInfo` with the data extracted from `ctx`
+func ExtractAuthInfo(ctx context.Context) (*AuthInfo, error) {
+	token, err := grpc_auth.AuthFromMD(ctx, "bearer")
+
+	if err != nil {
+		return nil, err
+	}
+
+	split := strings.SplitN(string(token), ".", 3)
+
+	// v1 is base64-encoded using base64.StdEncoding, which cannot contain a ".".
+	// A v1 token cannot slip through here.
+	if len(split) != 3 {
+		return &AuthInfo{Version: "v1", Message: token}, nil
+	}
+
+	version, sig, msg := split[0], split[1], split[2]
+	decodedSig, err := hex.DecodeString(sig)
+	if err != nil {
+		return nil, err
+	}
+
+	return &AuthInfo{Version: version, SignedMessage: decodedSig, Message: msg}, nil
+}
+
+func hmacInfoValid(message string, signedMessage, secret []byte, targetTime time.Time, timestampThreshold time.Duration) bool {
+	expectedHMAC := hmacSign(secret, message)
+	if !hmac.Equal(signedMessage, expectedHMAC) {
+		return false
+	}
+
+	timestamp, err := strconv.ParseInt(message, 10, 64)
+	if err != nil {
+		return false
+	}
+
+	issuedAt := time.Unix(timestamp, 0)
+	lowerBound := targetTime.Add(-timestampThreshold)
+	upperBound := targetTime.Add(timestampThreshold)
+
+	return issuedAt.After(lowerBound) && issuedAt.Before(upperBound)
+}
+
+func hmacSign(secret []byte, message string) []byte {
+	mac := hmac.New(sha256.New, secret)
+	mac.Write([]byte(message))
+
+	return mac.Sum(nil)
+}