diff --git a/context.go b/context.go
index fb7960d..ce299fb 100644
--- a/context.go
+++ b/context.go
@@ -18,3 +18,7 @@ type MutationCtx struct {
 	AuthCtx *AuthCtx
 	Params  map[string]interface{}
 }
+
+type Auth interface {
+	GetUserID(token string) (string, error)
+}
diff --git a/engine.go b/engine.go
index 324d7da..480674f 100644
--- a/engine.go
+++ b/engine.go
@@ -20,15 +20,20 @@ type Engine struct {
 	hashMu       sync.RWMutex
 	queryHashes  map[string]uint64
 	tracker      *reactivity.Tracker
+	auth         Auth
 }
 
+type defaultAuth struct{}
+
+func (defaultAuth) GetUserID(_ string) (string, error) { return "", nil }
+
 func NewEngine(db *gorm.DB, dbType string) *Engine {
 	slog.SetLogLoggerLevel(slog.LevelDebug)
 	tracker := reactivity.NewTracker()
 	if dbType != "sqlite" && dbType != "postgres" {
 		panic("Invalid database type")
 	}
-	e := &Engine{db: db, dbType: dbType, mutations: make(map[string]func(ctx *MutationCtx) interface{}), queries: make(map[string]func(ctx *QueryCtx) interface{}), dependencies: make(map[string][]string), queryHashes: make(map[string]uint64), tracker: tracker}
+	e := &Engine{db: db, dbType: dbType, mutations: make(map[string]func(ctx *MutationCtx) interface{}), queries: make(map[string]func(ctx *QueryCtx) interface{}), dependencies: make(map[string][]string), queryHashes: make(map[string]uint64), tracker: tracker, auth: defaultAuth{}}
 	db.Callback().Create().After("gorm:create").Register("tether:after_create", func(tx *gorm.DB) {
 		if dbType == "postgres" {
 			return
@@ -38,6 +43,10 @@ func NewEngine(db *gorm.DB, dbType string) *Engine {
 	return e
 }
 
+func (e *Engine) SetAuth(auth Auth) {
+	e.auth = auth
+}
+
 func (e *Engine) RegisterMutation(name string, mutation func(ctx *MutationCtx) interface{}) {
 	e.mutations[name] = mutation // stores the mutation in the list of valid mutations
 	slog.Debug("Registered mutation", "name", name)
@@ -200,6 +209,13 @@ func (e *Engine) OnReceiveMessage(clientID string, msg map[string]interface{}) e
 		e.ExecuteQuery(msg["location"].(string), msg["params"].(map[string]interface{}), clientID, true)
 	case "mutation":
 		e.ExecuteMutation(msg["location"].(string), msg["params"].(map[string]interface{}), clientID, msg["mutation_id"].(string))
+	case "auth":
+		userID, err := e.auth.GetUserID(msg["token"].(string))
+		if err != nil {
+			slog.Error("Failed to get user ID", "error", err)
+			return err
+		}
+		e.tracker.SetAuthID(clientID, userID)
 	}
 	return nil
 }