Support customizing session cookie name.

internal/home/authhttp.go

@@ -22,8 +22,11 @@ import (
 // cookieTTL is the time-to-live of the session cookie.
 const cookieTTL = 365 * timeutil.Day
 
+// defaultSessionCookieName is the default name of the session cookie.
+const defaultSessionCookieName = "agh_session"
+
 // sessionCookieName is the name of the session cookie.
-const sessionCookieName = "agh_session"
+var sessionCookieName = defaultSessionCookieName
 
 // loginJSON is the JSON structure for authentication.
 type loginJSON struct {

internal/home/home.go

@@ -15,6 +15,7 @@ import (
 	"path/filepath"
 	"runtime"
 	"slices"
+	"strings"
 	"sync"
 	"syscall"
 	"time"
@@ -270,6 +271,14 @@ func setupOpts(opts options) (err error) {
 	return nil
 }
 
+// setupAghUISettings sets up some AdGuard Home UI settings.
+func setupAghUISettings(opts options) {
+	cookieName := strings.TrimSpace(opts.sessionCookieName)
+	if cookieName != "" {
+		sessionCookieName = cookieName
+	}
+}
+
 // initContextClients initializes Context clients and related fields.
 func initContextClients() (err error) {
 	err = setupDNSFilteringConf(config.Filtering)
@@ -573,6 +582,8 @@ func run(opts options, clientBuildFS fs.FS, done chan struct{}) {
 	err = setupOpts(opts)
 	fatalOnError(err)
 
+	setupAghUISettings(opts)
+
 	execPath, err := os.Executable()
 	fatalOnError(errors.Annotate(err, "getting executable path: %w"))
 

internal/home/options.go

@@ -48,6 +48,10 @@ type options struct {
 	// bindAddr is the address to serve the web UI on.
 	bindAddr netip.AddrPort
 
+	// sessionCookieName is the name of the session cookie for the web UI.
+    // Customizing this value can prevent cookie key conflict for multiple AdGuardHome instances that have the same domain.
+    sessionCookieName string
+
 	// checkConfig is true if the current invocation is only required to check
 	// the configuration file and exit.
 	checkConfig bool
@@ -196,6 +200,18 @@ var cmdLineOpts = []cmdLineOpt{{
 	description: "Address to serve the web UI on, in the host:port format.",
 	longName:    "web-addr",
 	shortName:   "",
+}, {
+    updateWithValue: func(o options, v string) (oo options, err error) {
+        o.sessionCookieName = v
+
+        return o, nil
+    },
+    updateNoValue:   nil,
+    effect:          nil,
+    serialize:       func(o options) (val string, ok bool) { return o.sessionCookieName, o.sessionCookieName != "" },
+    description:     "Customize the session cookie name for the web UI.",
+    longName:        "session-cookie-name",
+    shortName:       "",
 }, {
 	updateWithValue: func(o options, v string) (options, error) {
 		o.serviceControlAction = v