android: Add utility that converts a Base64 string to a X509Certificate

src/frontends/android/app/src/main/java/org/strongswan/android/utils/Certificates.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2023 Relution GmbH
+ *
+ * Copyright (C) secunet Security Networks AG
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * 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.
+ */
+
+package org.strongswan.android.utils;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.security.cert.CertificateException;
+import java.security.cert.CertificateFactory;
+import java.security.cert.X509Certificate;
+
+import androidx.annotation.NonNull;
+
+public class Certificates
+{
+	@NonNull
+	public static X509Certificate from(@NonNull final String certificateData) throws IOException, CertificateException
+	{
+		final byte[] bytes = android.util.Base64.decode(certificateData, android.util.Base64.DEFAULT);
+
+		try (final ByteArrayInputStream stream = new ByteArrayInputStream(bytes))
+		{
+			final CertificateFactory certificateFactory = CertificateFactory.getInstance("X.509");
+			return (X509Certificate)certificateFactory.generateCertificate(stream);
+		}
+	}
+
+	private Certificates() {}
+}