Merge pull request #138 from MichaelEischer/cache-basic-auth

Cache basic auth credentials

changelog/unreleased/issue-133

@@ -0,0 +1,9 @@
+Enhancement: Cache basic auth credentials
+
+To speed up the verification of basic auth credentials, rest-server now caches
+passwords for a minute in memory. That way the expensive verification of basic
+auth credentials can be skipped for most requests issued by a single restic
+run. The password is kept in memory in a hashed form and not as plaintext.
+
+https://github.com/restic/rest-server/issues/133
+https://github.com/restic/rest-server/pull/138

htpasswd.go

@@ -26,6 +26,8 @@ THE SOFTWARE.
 
 import (
 	"crypto/sha1"
+	"crypto/sha256"
+	"crypto/subtle"
 	"encoding/base64"
 	"encoding/csv"
 	"log"
@@ -42,15 +44,26 @@ import (
 // CheckInterval represents how often we check for changes in htpasswd file.
 const CheckInterval = 30 * time.Second
 
+// PasswordCacheDuration represents how long authentication credentials are
+// cached in memory after they were successfully verified. This allows avoiding
+// repeatedly verifying the same authentication credentials.
+const PasswordCacheDuration = time.Minute
+
 // Lookup passwords in a htpasswd file.  The entries must have been created with -s for SHA encryption.
 
+type cacheEntry struct {
+	expiry   time.Time
+	verifier []byte
+}
+
 // HtpasswdFile is a map for usernames to passwords.
 type HtpasswdFile struct {
 	mutex    sync.Mutex
 	path     string
 	stat     os.FileInfo
 	throttle chan struct{}
-	Users    map[string]string
+	users    map[string]string
+	cache    map[string]cacheEntry
 }
 
 // NewHtpasswdFromFile reads the users and passwords from a htpasswd file and returns them.  If an error is encountered,
@@ -68,6 +81,7 @@ func NewHtpasswdFromFile(path string) (*HtpasswdFile, error) {
 		path:     path,
 		stat:     stat,
 		throttle: make(chan struct{}),
+		cache:    make(map[string]cacheEntry),
 	}
 
 	if err := h.Reload(); err != nil {
@@ -76,6 +90,7 @@ func NewHtpasswdFromFile(path string) (*HtpasswdFile, error) {
 
 	// Start a goroutine that limits reload checks to once per CheckInterval
 	go h.throttleTimer()
+	go h.expiryTimer()
 
 	go func() {
 		for range c {
@@ -100,6 +115,23 @@ func (h *HtpasswdFile) throttleTimer() {
 	}
 }
 
+func (h *HtpasswdFile) expiryTimer() {
+	for {
+		time.Sleep(5 * time.Second)
+		now := time.Now()
+		h.mutex.Lock()
+		var zeros [sha256.Size]byte
+		// try to wipe expired cache entries
+		for user, entry := range h.cache {
+			if entry.expiry.After(now) {
+				copy(entry.verifier, zeros[:])
+				delete(h.cache, user)
+			}
+		}
+		h.mutex.Unlock()
+	}
+}
+
 var validUsernameRegexp = regexp.MustCompile(`^[\p{L}\d@._-]+$`)
 
 // Reload reloads the htpasswd file. If the reload fails, the Users map is not changed and the error is returned.
@@ -130,7 +162,14 @@ func (h *HtpasswdFile) Reload() error {
 
 	// Replace the Users map
 	h.mutex.Lock()
-	h.Users = users
+	var zeros [sha256.Size]byte
+	// try to wipe the old cache entries
+	for _, entry := range h.cache {
+		copy(entry.verifier, zeros[:])
+	}
+	h.cache = make(map[string]cacheEntry)
+
+	h.users = users
 	h.mutex.Unlock()
 
 	_ = r.Close()
@@ -172,35 +211,74 @@ func (h *HtpasswdFile) ReloadCheck() error {
 	return nil
 }
 
+var shaRe = regexp.MustCompile(`^{SHA}`)
+var bcrRe = regexp.MustCompile(`^\$2b\$|^\$2a\$|^\$2y\$`)
+
 // Validate returns true if password matches the stored password for user.  If no password for user is stored, or the
 // password is wrong, false is returned.
 func (h *HtpasswdFile) Validate(user string, password string) bool {
 	_ = h.ReloadCheck()
 
+	hash := sha256.New()
+	// hash.Write can never fail
+	_, _ = hash.Write([]byte(user))
+	_, _ = hash.Write([]byte(":"))
+	_, _ = hash.Write([]byte(password))
+
 	h.mutex.Lock()
-	realPassword, exists := h.Users[user]
+	// avoid race conditions with cache replacements
+	cache := h.cache
+	hashedPassword, exists := h.users[user]
+	entry, cacheExists := h.cache[user]
 	h.mutex.Unlock()
 
 	if !exists {
 		return false
 	}
 
-	var shaRe = regexp.MustCompile(`^{SHA}`)
-	var bcrRe = regexp.MustCompile(`^\$2b\$|^\$2a\$|^\$2y\$`)
+	if cacheExists && subtle.ConstantTimeCompare(entry.verifier, hash.Sum(nil)) == 1 {
+		h.mutex.Lock()
+		// repurpose mutex to prevent concurrent cache updates
+		// extend cache entry
+		cache[user] = cacheEntry{
+			verifier: entry.verifier,
+			expiry:   time.Now().Add(PasswordCacheDuration),
+		}
+		h.mutex.Unlock()
+		return true
+	}
 
+	isValid := isMatchingHashAndPassword(hashedPassword, password)
+
+	if !isValid {
+		log.Printf("Invalid htpasswd entry for %s.", user)
+		return false
+	}
+
+	h.mutex.Lock()
+	// repurpose mutex to prevent concurrent cache updates
+	cache[user] = cacheEntry{
+		verifier: hash.Sum(nil),
+		expiry:   time.Now().Add(PasswordCacheDuration),
+	}
+	h.mutex.Unlock()
+
+	return true
+}
+
+func isMatchingHashAndPassword(hashedPassword string, password string) bool {
 	switch {
-	case shaRe.MatchString(realPassword):
+	case shaRe.MatchString(hashedPassword):
 		d := sha1.New()
 		_, _ = d.Write([]byte(password))
-		if realPassword[5:] == base64.StdEncoding.EncodeToString(d.Sum(nil)) {
+		if subtle.ConstantTimeCompare([]byte(hashedPassword[5:]), []byte(base64.StdEncoding.EncodeToString(d.Sum(nil)))) == 1 {
 			return true
 		}
-	case bcrRe.MatchString(realPassword):
-		err := bcrypt.CompareHashAndPassword([]byte(realPassword), []byte(password))
+	case bcrRe.MatchString(hashedPassword):
+		err := bcrypt.CompareHashAndPassword([]byte(hashedPassword), []byte(password))
 		if err == nil {
 			return true
 		}
 	}
-	log.Printf("Invalid htpasswd entry for %s.", user)
 	return false
 }

htpasswd_test.go

@@ -0,0 +1,46 @@
+package restserver
+
+import (
+	"io/ioutil"
+	"os"
+	"testing"
+)
+
+func TestValidate(t *testing.T) {
+	user := "restic"
+	pwd := "$2y$05$z/OEmNQamd6m6LSegUErh.r/Owk9Xwmc5lxDheIuHY2Z7XiS6FtJm"
+	rawPwd := "test"
+	wrongPwd := "wrong"
+
+	tmpfile, err := ioutil.TempFile("", "rest-validate-")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err = tmpfile.Write([]byte(user + ":" + pwd + "\n")); err != nil {
+		t.Fatal(err)
+	}
+	if err = tmpfile.Close(); err != nil {
+		t.Fatal(err)
+	}
+
+	htpass, err := NewHtpasswdFromFile(tmpfile.Name())
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	for i := 0; i < 10; i++ {
+		isValid := htpass.Validate(user, rawPwd)
+		if !isValid {
+			t.Fatal("correct password not accepted")
+		}
+
+		isValid = htpass.Validate(user, wrongPwd)
+		if isValid {
+			t.Fatal("wrong password accepted")
+		}
+	}
+
+	if err = os.Remove(tmpfile.Name()); err != nil {
+		t.Fatal(err)
+	}
+}