Authentication improvements/fixes

app/src/main/java/eu/faircode/email/ActivityBase.java

@@ -20,8 +20,10 @@ package eu.faircode.email;
 */
 
 import android.Manifest;
+import android.content.BroadcastReceiver;
 import android.content.Context;
 import android.content.Intent;
+import android.content.IntentFilter;
 import android.content.SharedPreferences;
 import android.content.res.Configuration;
 import android.os.Bundle;
@@ -84,6 +86,8 @@ abstract class ActivityBase extends AppCompatActivity implements SharedPreferenc
 
         prefs.registerOnSharedPreferenceChangeListener(this);
 
+        registerReceiver(onScreenOff, new IntentFilter(Intent.ACTION_SCREEN_OFF));
+
         super.onCreate(savedInstanceState);
     }
 
@@ -139,6 +143,7 @@ abstract class ActivityBase extends AppCompatActivity implements SharedPreferenc
     @Override
     protected void onDestroy() {
         Log.i("Destroy " + this.getClass().getName());
+        unregisterReceiver(onScreenOff);
         PreferenceManager.getDefaultSharedPreferences(this).unregisterOnSharedPreferenceChangeListener(this);
         super.onDestroy();
     }
@@ -163,6 +168,17 @@ abstract class ActivityBase extends AppCompatActivity implements SharedPreferenc
             finish();
     }
 
+    private BroadcastReceiver onScreenOff = new BroadcastReceiver() {
+        @Override
+        public void onReceive(Context context, Intent intent) {
+            Log.i(intent.toString());
+            Log.logExtras(intent);
+
+            SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(ActivityBase.this);
+            prefs.edit().remove("last_authentication").apply();
+        }
+    };
+
     public boolean hasPermission(String name) {
         return Helper.hasPermission(this, name);
     }