java/com/tailscale/ipn: upgrade Android security to support Android 5.1

As luck would have it, there's a new version of the androidx.security
library available that support Android 5+. Use that, and adjust to the
incompatible API changes.

Fixes tailscale/tailscale#577

Signed-off-by: Elias Naur <mail@eliasnaur.com>

android/build.gradle

@@ -23,7 +23,7 @@ apply plugin: 'com.android.application'
 android {
     compileSdkVersion 29
     defaultConfig {
-        minSdkVersion 23
+        minSdkVersion 22
         targetSdkVersion 29
         versionCode 16
         versionName System.getenv("VERSION")
@@ -38,6 +38,6 @@ dependencies {
 	implementation 'com.google.android.gms:play-services-auth:18.0.0'
 	implementation "androidx.core:core:1.2.0"
 	implementation "androidx.browser:browser:1.2.0"
-	implementation "androidx.security:security-crypto:1.0.0-rc01"
+	implementation "androidx.security:security-crypto:1.1.0-alpha02"
 	implementation ':ipn@aar'
 }

android/src/main/java/com/tailscale/ipn/App.java

@@ -25,7 +25,7 @@ import java.io.FileOutputStream;
 import java.security.GeneralSecurityException;
 
 import androidx.security.crypto.EncryptedSharedPreferences;
-import androidx.security.crypto.MasterKeys;
+import androidx.security.crypto.MasterKey;
 
 import org.gioui.Gio;
 
@@ -72,12 +72,14 @@ public class App extends Application {
 	}
 
 	private SharedPreferences getEncryptedPrefs() throws IOException, GeneralSecurityException {
-		String masterKeyAlias = MasterKeys.getOrCreate(MasterKeys.AES256_GCM_SPEC);
+		MasterKey key = new MasterKey.Builder(this)
+			.setKeyScheme(MasterKey.KeyScheme.AES256_GCM)
+			.build();
 
 		return EncryptedSharedPreferences.create(
-				"secret_shared_prefs",
-				masterKeyAlias,
 				this,
+				"secret_shared_prefs",
+				key,
 				EncryptedSharedPreferences.PrefKeyEncryptionScheme.AES256_SIV,
 				EncryptedSharedPreferences.PrefValueEncryptionScheme.AES256_GCM
 		);