fix: treat TokenSource JWTs without exp as expired (#1008)

CachingTokenSource.hasValidToken treated a missing exp as still valid, so TokenSourceCached never refetched. Require exp and keep nbf optional, matching client-sdk-js#2057.

Author: SashaMIT

.changeset/token-source-require-exp.md

@@ -0,0 +1,5 @@
+---
+"client-sdk-android": patch
+---
+
+Fix CachingTokenSource treating a JWT with no exp as still valid, so a token that never expires stays cached forever. Require exp; keep nbf optional.

livekit-android-sdk/src/main/java/io/livekit/android/token/CachingTokenSource.kt

@@ -151,11 +151,13 @@ fun TokenSourceResponse.hasValidToken(tolerance: Duration = 60.seconds, date: Da
     try {
         val jwt = TokenPayload(participantToken)
         val now = Date()
-        val expiresAt = jwt.expiresAt
+        // First-party minters always set exp. A signed JWT with no exp would
+        // otherwise stay cached forever (livekit/client-sdk-js#2057).
+        val expiresAt = jwt.expiresAt ?: return false
         val nbf = jwt.notBefore
 
         val isBefore = nbf != null && now.before(nbf)
-        val hasExpired = expiresAt != null && now.after(Date(expiresAt.time + tolerance.inWholeMilliseconds))
+        val hasExpired = now.after(Date(expiresAt.time + tolerance.inWholeMilliseconds))
 
         return !isBefore && !hasExpired
     } catch (e: Exception) {

livekit-android-test/src/test/java/io/livekit/android/token/CachingTokenSourceTest.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2025 LiveKit, Inc.
+ * Copyright 2025-2026 LiveKit, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@ import kotlinx.coroutines.ExperimentalCoroutinesApi
 import okhttp3.mockwebserver.MockResponse
 import okhttp3.mockwebserver.MockWebServer
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertFalse
 import org.junit.Assert.assertNotEquals
 import org.junit.Assert.assertTrue
 import org.junit.Test
@@ -63,6 +64,26 @@ class CachingTokenSourceTest : BaseTest() {
         assertTrue(tokenResponse.hasValidToken(date = Date(9999999990000)))
     }
 
+    @Test
+    fun tokenWithoutExpIsInvalid() {
+        val tokenResponse = TokenSourceResponse(
+            "wss://www.example.com",
+            NO_EXP_TOKEN,
+        )
+
+        assertFalse(tokenResponse.hasValidToken())
+    }
+
+    @Test
+    fun tokenWithExpOnlyIsValid() {
+        val tokenResponse = TokenSourceResponse(
+            "wss://www.example.com",
+            EXP_ONLY_TOKEN,
+        )
+
+        assertTrue(tokenResponse.hasValidToken())
+    }
+
     @Test
     fun cachedValidTokenOnlyFetchedOnce() = runTest {
         val server = MockWebServer()
@@ -128,5 +149,13 @@ class CachingTokenSourceTest : BaseTest() {
         const val EXPIRED_TOKEN = "eyJ0eXAiOiJKV1QiLCJhbGciOiJFUzI1NiIsImtpZCI6IjlhMzJiZTg2NzkyZTM3Nm" +
             "I3ZTBlMmIyNjVjMjY1YTA5In0.eyJpYXQiOjAsIm5iZiI6MCwiZXhwIjowfQ.8oV9K-CeULScAjFIK2O7sxEGUD7" +
             "su3kCQv3Q8rhk0Hg_AuzQixJfz2Pt0rJUwLWhF0mSlcYMUKdR0yp12RfrdA"
+
+        // Dummy HS256 JWTs for cache-validity only (signature is not verified).
+        // NO_EXP: {"sub":"identity"} with no exp.
+        // EXP_ONLY: same identity plus exp 9876543210 (Fri Dec 22 2282).
+        const val NO_EXP_TOKEN = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJpZGVudGl0eSJ9." +
+            "ytOOgz0Ly2PUjItxXAXFRIE9sgZnOKPzQVSovM7uH84"
+        const val EXP_ONLY_TOKEN = "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9." +
+            "eyJzdWIiOiJpZGVudGl0eSIsImV4cCI6OTg3NjU0MzIxMH0.Im7BMAH9ZdnkdPb7oTny_kEiVmdzep3Bl-SNwqAruMw"
     }
 }