Allow user CAs

app/src/main/res/xml/network_security_config.xml

+<?xml version="1.0" encoding="utf-8"?><!--
+  Quasseldroid - Quassel client for Android
+
+  Copyright (c) 2019 Janne Koschinski
+  Copyright (c) 2019 The Quassel Project
+
+  This program is free software: you can redistribute it and/or modify it
+  under the terms of the GNU General Public License version 3 as published
+  by the Free Software Foundation.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License along
+  with this program. If not, see <http://www.gnu.org/licenses/>.
+  -->
+
+<network-security-config>
+  <base-config cleartextTrafficPermitted="true">
+    <trust-anchors>
+      <!-- Trust preinstalled CAs -->
+      <certificates src="system" />
+      <!-- Additionally trust user added CAs -->
+      <certificates src="user" />
+    </trust-anchors>
+  </base-config>
+</network-security-config>