caddyauth: Speed up basicauth provisioning, precalculate fake password

modules/caddyhttp/caddyauth/basicauth.go

@@ -94,7 +94,7 @@ func (hba *HTTPBasicAuth) Provision(ctx caddy.Context) error {
 
 	// if supported, generate a fake password we can compare against if needed
 	if hasher, ok := hba.Hash.(Hasher); ok {
-		hba.fakePassword, err = hasher.Hash([]byte("antitiming"), []byte("fakesalt"))
+		hba.fakePassword = hasher.FakeHash()
 		if err != nil {
 			return fmt.Errorf("generating anti-timing password hash: %v", err)
 		}
@@ -271,9 +271,11 @@ type Comparer interface {
 // that require a salt). Hashing modules which implement
 // this interface can be used with the hash-password
 // subcommand as well as benefitting from anti-timing
-// features.
+// features. A hasher also returns a fake hash which
+// can be used for timing side-channel mitigation.
 type Hasher interface {
 	Hash(plaintext, salt []byte) ([]byte, error)
+	FakeHash() []byte
 }
 
 // Account contains a username, password, and salt (if applicable).

modules/caddyhttp/caddyauth/hashes.go

@@ -16,6 +16,7 @@ package caddyauth
 
 import (
 	"crypto/subtle"
+	"encoding/base64"
 
 	"github.com/caddyserver/caddy/v2"
 	"golang.org/x/crypto/bcrypt"
@@ -55,6 +56,14 @@ func (BcryptHash) Hash(plaintext, _ []byte) ([]byte, error) {
 	return bcrypt.GenerateFromPassword(plaintext, 14)
 }
 
+// FakeHash returns a fake hash.
+func (BcryptHash) FakeHash() []byte {
+	// hashed with the following command:
+	// caddy hash-password --plaintext "antitiming" --algorithm "bcrypt"
+	bytes, _ := base64.StdEncoding.DecodeString("JDJhJDE0JFgzdWxxZi9pR3huZjFrNm9NWi5SWmVKVW9xSTlQWDJQTTRyUzVsa0lLSlhkdUxHWEdQcnQ2")
+	return bytes
+}
+
 // ScryptHash implements the scrypt KDF as a hash.
 type ScryptHash struct {
 	// scrypt's N parameter. If unset or 0, a safe default is used.
@@ -123,6 +132,14 @@ func (s ScryptHash) Hash(plaintext, salt []byte) ([]byte, error) {
 	return scrypt.Key(plaintext, salt, s.N, s.R, s.P, s.KeyLength)
 }
 
+// FakeHash returns a fake hash.
+func (ScryptHash) FakeHash() []byte {
+	// hashed with the following command:
+	// caddy hash-password --plaintext "antitiming" --salt "fakesalt" --algorithm "scrypt"
+	bytes, _ := base64.StdEncoding.DecodeString("kFbjiVemlwK/ZS0tS6/UQqEDeaNMigyCs48KEsGUse8=")
+	return bytes
+}
+
 func hashesMatch(pwdHash1, pwdHash2 []byte) bool {
 	return subtle.ConstantTimeCompare(pwdHash1, pwdHash2) == 1
 }