Config: Improve preview token security

internal/config/auth.go

@@ -46,10 +46,10 @@ func (c *Config) InvalidPreviewToken(t string) bool {
 	return c.PreviewToken() != t && c.DownloadToken() != t
 }
 
-// PreviewToken returns the THUMBNAILS api token (you can optionally use a static value for permanent caching).
+// PreviewToken returns the preview image api token (based on the unique storage serial by default).
 func (c *Config) PreviewToken() string {
 	if c.options.PreviewToken == "" {
-		c.options.PreviewToken = rnd.Token(8)
+		c.options.PreviewToken = c.SerialChecksum()
 	}
 
 	return c.options.PreviewToken

internal/config/config.go

@@ -1,7 +1,9 @@
 package config
 
 import (
+	"encoding/hex"
 	"fmt"
+	"hash/crc32"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -141,6 +143,10 @@ func (c *Config) Init() error {
 
 // initStorage initializes storage directories with a random serial.
 func (c *Config) initStorage() error {
+	if c.serial != "" {
+		return nil
+	}
+
 	const serialName = "serial"
 
 	c.serial = rnd.PPID('z')
@@ -161,6 +167,28 @@ func (c *Config) initStorage() error {
 	return nil
 }
 
+// Serial returns the random storage serial.
+func (c *Config) Serial() string {
+	if err := c.initStorage(); err != nil {
+		log.Errorf("config: %s", err)
+	}
+
+	return c.serial
+}
+
+// SerialChecksum returns the CRC32 checksum of the storage serial.
+func (c *Config) SerialChecksum() string {
+	var result []byte
+
+	hash := crc32.New(crc32.MakeTable(crc32.Castagnoli))
+
+	if _, err := hash.Write([]byte(c.Serial())); err != nil {
+		log.Warnf("config: %s", err)
+	}
+
+	return hex.EncodeToString(hash.Sum(result))
+}
+
 // Name returns the application name ("PhotoPrism").
 func (c *Config) Name() string {
 	return c.options.Name

internal/config/config_test.go

@@ -304,3 +304,23 @@ func TestConfig_SiteTitle(t *testing.T) {
 	c.options.SiteTitle = "Cats"
 	assert.Equal(t, "Cats", c.SiteTitle())
 }
+
+func TestConfig_Serial(t *testing.T) {
+	c := NewConfig(CliTestContext())
+
+	result := c.Serial()
+
+	t.Logf("Serial: %s", result)
+
+	assert.NotEmpty(t, result)
+}
+
+func TestConfig_SerialChecksum(t *testing.T) {
+	c := NewConfig(CliTestContext())
+
+	result := c.SerialChecksum()
+
+	t.Logf("SerialChecksum: %s", result)
+
+	assert.NotEmpty(t, result)
+}

internal/config/flags.go

@@ -295,13 +295,12 @@ var GlobalFlags = []cli.Flag{
 	},
 	cli.StringFlag{
 		Name:   "download-token",
-		Usage:  "`SECRET` url token for file downloads",
+		Usage:  "optional static `SECRET` url token for file downloads",
 		EnvVar: "PHOTOPRISM_DOWNLOAD_TOKEN",
 	},
 	cli.StringFlag{
 		Name:   "preview-token",
-		Usage:  "`SECRET` url token for preview images and video streaming",
+		Usage:  "optional static `SECRET` url token for preview images and video streaming",
-		Value:  "public",
 		EnvVar: "PHOTOPRISM_PREVIEW_TOKEN",
 	},
 	cli.StringFlag{