Modify cache purging limit

digest.go

@@ -79,7 +79,8 @@ func (da *DigestAuth) Purge(count int) {
 	}
 	cache := digestCache(entries)
 	sort.Sort(cache)
-	for _, client := range cache[:count] {
+
+	for _, client := range cache {
 		delete(da.clients, client.nonce)
 	}
 }

digest_test.go

@@ -76,3 +76,28 @@ func TestDigestAuthParams(t *testing.T) {
 		t.Fatalf("failed to parse uri with embedded commas, got %q want %q", params["uri"], want)
 	}
 }
+
+// TestDigestPurge tests that when we purge clients from the authenticator we do not purge
+// more cache entries than the number of clients we have received.
+// This is to avoid regressing and hitting a "slice bounds out of range" panic.
+func TestDigestPurge(t *testing.T) {
+	t.Parallel()
+	// Creating dummy clients for the digest authenticator.
+	nClients := 10
+	clients := make(map[string]*digestClient, nClients)
+	for i := 0; i < nClients; i++ {
+		clients[string(i)] = &digestClient{}
+	}
+
+	secrets := HtdigestFileProvider("test.htdigest")
+	da := &DigestAuth{
+		Opaque:  "U7H+ier3Ae8Skd/g",
+		Realm:   "example.com",
+		Secrets: secrets,
+		clients: clients,
+	}
+
+	// Purging more than the number of clients we have stored in the
+	// digest authenticator.
+	da.Purge(nClients * 2)
+}