Lock Android app on background for biometrics

android/app/build.gradle

@@ -18,8 +18,8 @@ android {
         applicationId "net.linkedcorp.linkedsign"
         minSdk 26
         targetSdk 35
-        versionCode 10204
-        versionName "1.2.4"
+        versionCode 10205
+        versionName "1.2.5"
 
         buildConfigField "String", "API_BASE_URL", "\"${apiBaseUrl}\""
     }

android/app/src/main/java/net/linkedcorp/linkedsign/ui/LinkedSignApp.kt

@@ -95,6 +95,7 @@ import androidx.compose.material3.TopAppBar
 import androidx.compose.material3.TopAppBarDefaults
 import androidx.compose.material3.IconButton
 import androidx.compose.runtime.Composable
+import androidx.compose.runtime.DisposableEffect
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
@@ -113,6 +114,9 @@ import androidx.compose.ui.layout.ContentScale
 import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.platform.LocalContext
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleEventObserver
+import androidx.lifecycle.compose.LocalLifecycleOwner
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.input.KeyboardType
 import androidx.compose.ui.text.input.PasswordVisualTransformation
@@ -209,6 +213,7 @@ fun LinkedSignApp(viewModel: MainViewModel, appContext: Context, activity: Compo
     var selectedTab by rememberSaveable { mutableStateOf(AppTab.Documents) }
     var pendingSignDocumentId by rememberSaveable { mutableStateOf<String?>(null) }
     val biometricAvailable = remember(activity) { canUseBiometricAccess(activity) }
+    val lifecycleOwner = LocalLifecycleOwner.current
     var appUnlocked by rememberSaveable { mutableStateOf(false) }
     var bootstrapGateHandled by rememberSaveable { mutableStateOf(false) }
     var showBiometricOptIn by rememberSaveable { mutableStateOf(false) }
@@ -235,6 +240,23 @@ fun LinkedSignApp(viewModel: MainViewModel, appContext: Context, activity: Compo
         }
     }
 
+    DisposableEffect(lifecycleOwner, biometricAvailable, state.biometricEnabled, state.biometricHasCredentials) {
+        val observer = LifecycleEventObserver { _, event ->
+            if (event == Lifecycle.Event.ON_STOP &&
+                biometricAvailable &&
+                state.biometricEnabled &&
+                state.biometricHasCredentials
+            ) {
+                appUnlocked = false
+            }
+        }
+
+        lifecycleOwner.lifecycle.addObserver(observer)
+        onDispose {
+            lifecycleOwner.lifecycle.removeObserver(observer)
+        }
+    }
+
     Scaffold(
         modifier = Modifier.pointerInput(state.authenticated) {
             if (!state.authenticated) return@pointerInput