frontends/android: add an authentication feature

Watch-only can benefit from a feature that allows the user to authenticate
when opening the bitboxapp, to protect the privacy. This commit creates
an Auth component in the frontend that can trigger an environment-based
authentication.

On Qt and Webdev the authentication succeds automatically, while on Android
it requires the user to complete the system biometric authentication
every time the app is resumed (.i.e. at startup and when the app comes to
foreground after being put in the background).

The authentication can be requested by the frontend using the 'auth' endpoint.

Authentication messages from backend to frontend are sent via a new 'auth'
notifications, which contains a Typ string:
- 'auth-required': which triggers a new `auth` call from the frontend
- 'auth-ok': which means authentication completed successfully
- 'auth-err': which means authentication failed or has been cancelled
by the user.

Author: benma

backend/accounts_test.go

@@ -310,6 +310,8 @@ func (e environment) DetectDarkTheme() bool {
 	return false
 }
 
+func (e environment) Auth() {}
+
 func newBackend(t *testing.T, testing, regtest bool) *Backend {
 	t.Helper()
 	b, err := NewBackend(

backend/backend.go

@@ -112,6 +112,18 @@ type AccountEvent struct {
 	Data string             `json:"data"`
 }
 
+type authEventType string
+
+const (
+	authRequired authEventType = "auth-required"
+	authOk       authEventType = "auth-ok"
+	authErr      authEventType = "auth-err"
+)
+
+type authEventObject struct {
+	Typ authEventType `json:"typ"`
+}
+
 // Environment represents functionality where the implementation depends on the environment the app
 // runs in, e.g. Qt5/Mobile/webdev.
 type Environment interface {
@@ -143,6 +155,7 @@ type Environment interface {
 	SetDarkTheme(bool)
 	// DetectDarkTheme returns true if the dark theme is enabled at OS level.
 	DetectDarkTheme() bool
+	Auth()
 }
 
 // Backend ties everything together and is the main starting point to use the BitBox wallet library.
@@ -296,6 +309,31 @@ func (backend *Backend) Config() *config.Config {
 	return backend.config
 }
 
+func (backend *Backend) TriggerAuth() {
+	backend.Notify(observable.Event{
+		Subject: "auth",
+		Action:  action.Replace,
+		Object: authEventObject{
+			Typ: authRequired,
+		},
+	})
+}
+
+func (backend *Backend) AuthResult(ok bool) {
+	backend.log.Infof("Auth result: %v", ok)
+	typ := authErr
+	if ok {
+		typ = authOk
+	}
+	backend.Notify(observable.Event{
+		Subject: "auth",
+		Action:  action.Replace,
+		Object: authEventObject{
+			Typ: typ,
+		},
+	})
+}
+
 // DefaultAppConfig returns the default app config.
 func (backend *Backend) DefaultAppConfig() config.AppConfig {
 	return config.NewDefaultAppConfig()

backend/bridgecommon/bridgecommon.go

@@ -121,6 +121,27 @@ func HandleURI(uri string) {
 	globalBackend.HandleURI(uri)
 }
 
+// TriggerAuth triggers an authentication request notification.
+func TriggerAuth() {
+	mu.Lock()
+	defer mu.Unlock()
+	if globalBackend == nil {
+		return
+	}
+	globalBackend.TriggerAuth()
+}
+
+// AuthResult triggers an authentication result notification
+// on the base of the input value.
+func AuthResult(ok bool) {
+	mu.Lock()
+	defer mu.Unlock()
+	if globalBackend == nil {
+		return
+	}
+	globalBackend.AuthResult(ok)
+}
+
 // UsingMobileDataChanged should be called when the network connnection changed.
 func UsingMobileDataChanged() {
 	mu.RLock()
@@ -147,6 +168,7 @@ type BackendEnvironment struct {
 	GetSaveFilenameFunc func(string) string
 	SetDarkThemeFunc    func(bool)
 	DetectDarkThemeFunc func() bool
+	AuthFunc            func()
 }
 
 // NotifyUser implements backend.Environment.
@@ -156,6 +178,13 @@ func (env *BackendEnvironment) NotifyUser(text string) {
 	}
 }
 
+// Auth implements backend.Environment.
+func (env *BackendEnvironment) Auth() {
+	if env.AuthFunc != nil {
+		env.AuthFunc()
+	}
+}
+
 // DeviceInfos implements backend.Environment.
 func (env *BackendEnvironment) DeviceInfos() []usb.DeviceInfo {
 	if env.DeviceInfosFunc != nil {

backend/bridgecommon/bridgecommon_test.go

@@ -69,6 +69,8 @@ func (e environment) DetectDarkTheme() bool {
 	return false
 }
 
+func (e environment) Auth() {}
+
 // TestServeShutdownServe checks that you can call Serve twice in a row.
 func TestServeShutdownServe(t *testing.T) {
 	bridgecommon.Serve(

backend/handlers/handlers.go

@@ -194,6 +194,7 @@ func NewHandlers(
 	getAPIRouterNoError(apiRouter)("/update", handlers.getUpdateHandler).Methods("GET")
 	getAPIRouterNoError(apiRouter)("/banners/{key}", handlers.getBannersHandler).Methods("GET")
 	getAPIRouterNoError(apiRouter)("/using-mobile-data", handlers.getUsingMobileDataHandler).Methods("GET")
+	getAPIRouterNoError(apiRouter)("/auth", handlers.getAuthHandler).Methods("GET")
 	getAPIRouter(apiRouter)("/set-dark-theme", handlers.postDarkThemeHandler).Methods("POST")
 	getAPIRouterNoError(apiRouter)("/detect-dark-theme", handlers.getDetectDarkThemeHandler).Methods("GET")
 	getAPIRouterNoError(apiRouter)("/version", handlers.getVersionHandler).Methods("GET")
@@ -459,6 +460,12 @@ func (handlers *Handlers) getUsingMobileDataHandler(r *http.Request) interface{}
 	return handlers.backend.Environment().UsingMobileData()
 }
 
+func (handlers *Handlers) getAuthHandler(r *http.Request) interface{} {
+	handlers.log.Info("Auth requested")
+	handlers.backend.Environment().Auth()
+	return nil
+}
+
 func (handlers *Handlers) postDarkThemeHandler(r *http.Request) (interface{}, error) {
 	var isDark bool
 	if err := json.NewDecoder(r.Body).Decode(&isDark); err != nil {

backend/handlers/handlers_test.go

@@ -58,6 +58,7 @@ func (e *backendEnv) NativeLocale() string          { return e.Locale }
 func (e *backendEnv) GetSaveFilename(string) string { return "" }
 func (e *backendEnv) SetDarkTheme(bool)             {}
 func (e *backendEnv) DetectDarkTheme() bool         { return false }
+func (e *backendEnv) Auth()                         {}
 
 func TestGetNativeLocale(t *testing.T) {
 	const ptLocale = "pt"

cmd/servewallet/main.go

@@ -23,7 +23,7 @@ import (
 	"runtime"
 	"strings"
 
-	"github.com/digitalbitbox/bitbox-wallet-app/backend"
+	backendPkg "github.com/digitalbitbox/bitbox-wallet-app/backend"
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/arguments"
 	btctypes "github.com/digitalbitbox/bitbox-wallet-app/backend/coins/btc/types"
 	"github.com/digitalbitbox/bitbox-wallet-app/backend/devices/usb"
@@ -39,6 +39,8 @@ const (
 	address = "0.0.0.0"
 )
 
+var backend *backendPkg.Backend
+
 // webdevEnvironment implements backend.Environment.
 type webdevEnvironment struct {
 }
@@ -80,6 +82,16 @@ func (webdevEnvironment) UsingMobileData() bool {
 	return false
 }
 
+// Auth implements backend.Environment.
+func (webdevEnvironment) Auth() {
+	log := logging.Get().WithGroup("servewallet")
+	log.Info("Webdev Auth")
+	if backend != nil {
+		backend.AuthResult(true)
+		log.Info("Webdev Auth OK")
+	}
+}
+
 // NativeLocale naively implements backend.Environment.
 // This version is unlikely to work on Windows.
 func (webdevEnvironment) NativeLocale() string {
@@ -141,7 +153,7 @@ func main() {
 	log.Info("--------------- Started application --------------")
 	// since we are in dev-mode, we can drop the authorization token
 	connectionData := backendHandlers.NewConnectionData(-1, "")
-	backend, err := backend.NewBackend(
+	newBackend, err := backendPkg.NewBackend(
 		arguments.NewArguments(
 			config.AppDir(),
 			!*mainnet,
@@ -153,6 +165,7 @@ func main() {
 	if err != nil {
 		log.WithField("error", err).Panic(err)
 	}
+	backend = newBackend
 	handlers := backendHandlers.NewHandlers(backend, connectionData)
 	log.WithFields(logrus.Fields{"address": address, "port": port}).Info("Listening for HTTP")
 	fmt.Printf("Listening on: http://localhost:%d\n", port)

frontends/android/BitBoxApp/app/build.gradle

@@ -28,6 +28,7 @@ android {
 dependencies {
     implementation fileTree(dir: 'libs', include: ['*.jar'])
     implementation 'androidx.appcompat:appcompat:1.0.2'
+    implementation 'androidx.biometric:biometric:1.1.0'
     implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
     testImplementation 'junit:junit:4.12'
     androidTestImplementation 'androidx.test:runner:1.2.0'

frontends/android/BitBoxApp/app/src/main/java/ch/shiftcrypto/bitboxapp/BiometricAuthHelper.java

@@ -0,0 +1,53 @@
+package ch.shiftcrypto.bitboxapp;
+
+import android.os.Handler;
+import android.os.Looper;
+
+import androidx.annotation.NonNull;
+import androidx.biometric.BiometricManager;
+import androidx.biometric.BiometricPrompt;
+import androidx.core.content.ContextCompat;
+import androidx.fragment.app.FragmentActivity;
+
+import java.util.concurrent.Executor;
+
+public class BiometricAuthHelper {
+
+    public interface AuthCallback {
+        void onSuccess();
+        void onFailure();
+    }
+
+    public static void showAuthenticationPrompt(FragmentActivity activity, AuthCallback callback) {
+        Executor executor = ContextCompat.getMainExecutor(activity);
+        BiometricPrompt biometricPrompt = new BiometricPrompt(activity, executor, new BiometricPrompt.AuthenticationCallback() {
+            @Override
+            public void onAuthenticationSucceeded(BiometricPrompt.AuthenticationResult result) {
+                super.onAuthenticationSucceeded(result);
+                new Handler(Looper.getMainLooper()).post(callback::onSuccess);
+            }
+
+            @Override
+            public void onAuthenticationFailed() {
+                super.onAuthenticationFailed();
+                new Handler(Looper.getMainLooper()).post(callback::onFailure);
+            }
+
+            @Override
+            public void onAuthenticationError(int errorCode, @NonNull CharSequence errString) {
+                Util.log("Authentication error: " + errorCode + " - " + errString);
+                super.onAuthenticationError(errorCode, errString);
+                new Handler(Looper.getMainLooper()).post(callback::onFailure);
+            }
+        });
+
+        BiometricPrompt.PromptInfo promptInfo = new BiometricPrompt.PromptInfo.Builder()
+                .setTitle("Authentication required")
+                .setAllowedAuthenticators(BiometricManager.Authenticators.DEVICE_CREDENTIAL |
+                                BiometricManager.Authenticators.BIOMETRIC_WEAK)
+                .setConfirmationRequired(false)
+                .build();
+
+        biometricPrompt.authenticate(promptInfo);
+    }
+}

frontends/android/BitBoxApp/app/src/main/java/ch/shiftcrypto/bitboxapp/GoViewModel.java

@@ -121,6 +121,11 @@ public void systemOpen(String url) throws Exception {
             Util.systemOpen(getApplication(), url);
         }
 
+        public void auth() {
+            Util.log("Auth requested from backend");
+            requestAuth();
+        }
+
         public boolean usingMobileData() {
             // Adapted from https://stackoverflow.com/a/53243938
 
@@ -187,15 +192,29 @@ public void pushNotify(String msg) {
         }
     }
 
-     private MutableLiveData<Boolean> isDarkTheme = new MutableLiveData<>();
+    private MutableLiveData<Boolean> isDarkTheme = new MutableLiveData<>();
 
-     public MutableLiveData<Boolean> getIsDarkTheme() {
+    public MutableLiveData<Boolean> getIsDarkTheme() {
          return isDarkTheme;
      }
-
-     public void setIsDarkTheme(Boolean isDark) {
+    public void setIsDarkTheme(Boolean isDark) {
          this.isDarkTheme.postValue(isDark);
     }
+
+    private MutableLiveData<Boolean> authenticator = new MutableLiveData<>(false);
+
+    public MutableLiveData<Boolean> getAuthenticator() {
+        return authenticator;
+    }
+
+    public void requestAuth() {
+        this.authenticator.postValue(true);
+    }
+
+    public void closeAuth() {
+        this.authenticator.postValue(false);
+    }
+
     private GoEnvironment goEnvironment;
     private GoAPI goAPI;