Allow server to receive an hmac token with the client timestamp for auth

3 files changed, 180 insertions, 11 deletions

diff --git a/auth/extract_test.go b/auth/extract_test.go
index f2cc3f773..7d6df8fb0 100644
--- a/auth/extract_test.go
+++ b/auth/extract_test.go
@@ -2,7 +2,9 @@ package gitalyauth
 
 import (
 	"testing"
+	"time"
 
+	"github.com/grpc-ecosystem/go-grpc-middleware/util/metautils"
 	"github.com/stretchr/testify/require"
 	"golang.org/x/net/context"
 	"google.golang.org/grpc/codes"
@@ -11,7 +13,7 @@ import (
 	"google.golang.org/grpc/status"
 )
 
-func TestCheckToken(t *testing.T) {
+func TestCheckTokenV1(t *testing.T) {
 	secret := "secret 1234"
 
 	testCases := []struct {
@@ -44,13 +46,75 @@ func TestCheckToken(t *testing.T) {
 	for _, tc := range testCases {
 		t.Run(tc.desc, func(t *testing.T) {
 			ctx := metadata.NewIncomingContext(context.Background(), tc.md)
-			err := CheckToken(ctx, secret)
+			err := CheckToken(ctx, secret, time.Now())
 			require.Equal(t, tc.code, status.Code(err), "expected grpc code in error %v", err)
 		})
 	}
 
 }
 
+func TestCheckTokenV2(t *testing.T) {
+	targetTime := time.Unix(1535671600, 0)
+	secret := []byte("foo")
+
+	testCases := []struct {
+		desc   string
+		token  string
+		result error
+	}{
+		{
+			desc:   "Valid v2 secret, future time within threshold",
+			token:  "v2.3346cb25ecdb928defd368e7390522a86764bbdf1e8b21aaef27c4c23ec9c899.1535671615",
+			result: nil,
+		},
+		{
+			desc:   "Valid v2 secret, past time within threshold",
+			token:  "v2.b77158328e80be2984eaf08788419d25f3484eae484aec1297af6bdf1a456610.1535671585",
+			result: nil,
+		},
+		{
+			desc:   "Invalid secret, time within threshold",
+			token:  "v2.52a3b9016f46853c225c72b87617ac27109bba8a3068002069ab90e28253a911.1535671585",
+			result: errDenied,
+		},
+		{
+			desc:   "Valid secret, time too much in the future",
+			token:  "v2.ab9e7315aeecf6815fc0df585370157814131acab376f41797ad4ebc4d9a823c.1535671631",
+			result: errDenied,
+		},
+		{
+			desc:   "Valid secret, time too much in the past",
+			token:  "v2.f805bc69ca3aedd99e814b3fb1fc1e6a1094191691480b168a20fad7c2d24557.1535671569",
+			result: errDenied,
+		},
+		{
+			desc:   "Mismatching signed and clear message",
+			token:  "v2.319b96a3194c1cb2a2e6f1386161aca1c4cda13257fa9df8a328ab6769649bb0.1535671599",
+			result: errDenied,
+		},
+		{
+			desc:   "Invalid version",
+			token:  "v3.6fec98e8fe494284ce545c4b421799f02b9718b0eadfc3772d027e1ac5d6d569.1535671601",
+			result: errDenied,
+		},
+		{
+			desc:   "Empty token",
+			token:  "",
+			result: errDenied,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.desc, func(t *testing.T) {
+			md := metautils.NiceMD{}
+			md.Set("authorization", "Bearer "+tc.token)
+			result := CheckToken(md.ToIncoming(context.Background()), string(secret), targetTime)
+
+			require.Equal(t, tc.result, result)
+		})
+	}
+}
+
 func credsMD(t *testing.T, creds credentials.PerRPCCredentials) metadata.MD {
 	md, err := creds.GetRequestMetadata(context.Background())
 	require.NoError(t, err)
diff --git a/auth/rpccredentials.go b/auth/rpccredentials.go
index cbe94c253..c35cd4d61 100644
--- a/auth/rpccredentials.go
+++ b/auth/rpccredentials.go
@@ -2,6 +2,9 @@ package gitalyauth
 
 import (
 	"encoding/base64"
+	"fmt"
+	"strconv"
+	"time"
 
 	"golang.org/x/net/context"
 	"google.golang.org/grpc/credentials"
@@ -23,3 +26,31 @@ func (*rpcCredentials) RequireTransportSecurity() bool { return false }
 func (rc *rpcCredentials) GetRequestMetadata(context.Context, ...string) (map[string]string, error) {
 	return map[string]string{"authorization": "Bearer " + rc.token}, nil
 }
+
+// RPCCredentialsV2 can be used with grpc.WithPerRPCCredentials to create a
+// grpc.DialOption that inserts an HMAC token with the current timestamp
+// for authentication with a Gitaly server.
+func RPCCredentialsV2(token string) credentials.PerRPCCredentials {
+	return &rpcCredentialsV2{token: token}
+}
+
+type rpcCredentialsV2 struct {
+	token string
+}
+
+func (*rpcCredentialsV2) RequireTransportSecurity() bool { return false }
+
+func (rc *rpcCredentialsV2) GetRequestMetadata(context.Context, ...string) (map[string]string, error) {
+	return map[string]string{"authorization": "Bearer " + rc.hmacToken()}, nil
+}
+
+func (rc *rpcCredentialsV2) hmacToken() string {
+	return hmacToken("v2", []byte(rc.token), time.Now())
+}
+
+func hmacToken(version string, secret []byte, timestamp time.Time) string {
+	intTime := timestamp.Unix()
+	signedTimestamp := hmacSign(secret, strconv.FormatInt(intTime, 10))
+
+	return fmt.Sprintf("%s.%x.%d", version, signedTimestamp, intTime)
+}
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)
+}