OF-2883: Add fallback to older style base64 encoding for security.xml

In Openfire 4.9.0, the base64 encoder was changed. This causes a compatibility issue with security.xml files that
were generated by older values, that use the 'MIME' type of decoding (with linebreaks) that's not used in later versions.
While persisting data in 'security.xml', linebreaks are replaced by white space.

With the changes in this commit, the decoder checks for white space, and uses the older-style type of decoding when found.

xmppserver/src/main/java/org/jivesoftware/util/AesEncryptor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2017-2024 Ignite Realtime Foundation. All rights reserved.
+ * Copyright (C) 2017-2025 Ignite Realtime Foundation. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@
 import java.nio.charset.StandardCharsets;
 import java.security.Key;
 import java.security.Security;
+import java.util.Base64;
 
 /**
  * Utility class providing symmetric AES encryption/decryption. To strengthen
@@ -97,7 +98,17 @@ public String decrypt(String value) {
     @Override
     public String decrypt(String value, byte[] iv) {
         if (value == null) { return null; }
-        byte [] bytes = cipher(java.util.Base64.getDecoder().decode(value), getKey(), iv == null ? INIT_PARM : iv, Cipher.DECRYPT_MODE);
+
+        // OF-2883: In Openfire 4.9.0, the base64 encoder was changed. This causes a compatibility issue with security.xml files that
+        // were generated by older values, that use the 'MIME' type of decoding (with linebreaks) that's not used in later versions.
+        // While persisting data in 'security.xml', linebreaks are replaced by white space.
+        final Base64.Decoder decoder;
+        if (value.length() > 76 && Character.isWhitespace(value.charAt(76))) {
+            decoder = Base64.getMimeDecoder(); // Value saved by older version of Openfire.
+        } else {
+            decoder = Base64.getDecoder();
+        }
+        byte [] bytes = cipher(decoder.decode(value), getKey(), iv == null ? INIT_PARM : iv, Cipher.DECRYPT_MODE);
         if (bytes == null) { return null; }
         return new String(bytes, StandardCharsets.UTF_8);
     }

xmppserver/src/test/java/org/jivesoftware/util/AesEncryptorTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2017-2023 Ignite Realtime Foundation. All rights reserved.
+ * Copyright (C) 2017-2025 Ignite Realtime Foundation. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -101,4 +101,43 @@ public void testEncryptionWithKeyAndBadIV() {
 
     }
 
+    /**
+     * Tests decoding a Base64 value stored as would be stored in security.xml by versions of Openfire prior to 4.9.0.
+     *
+     * @see <a href="https://igniterealtime.atlassian.net/browse/OF-2883">OF-2883: Base64 decoding issue preventing startup (after upgrade to 4.9.0)</a>
+     */
+    @Test
+    public void testBase64DecodeValuePriorTo490()
+    {
+        // Setup text fixture.
+        final String unencoded = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod";
+        final String base64encoded = "PwwA2Ejt1HDS0xwbEg4qMzk/E9fDA1aA6TdL2zBPMVtwW9C2UnUafAmm/twRZxY89euheVg0rxoQ Vfo5to825asMcx/bJNPY136oZstULDU=";
+
+        // Execute system under test.
+        final AesEncryptor encryptor = new AesEncryptor();
+        final String result = encryptor.decrypt(base64encoded);
+
+        // Verify results.
+        assertEquals(unencoded, result);
+    }
+
+    /**
+     * Tests decoding a Base64 value stored as would be stored in security.xml by versions of Openfire 4.9.0 and later.
+     *
+     * @see <a href="https://igniterealtime.atlassian.net/browse/OF-2883">OF-2883: Base64 decoding issue preventing startup (after upgrade to 4.9.0)</a>
+     */
+    @Test
+    public void testBase64DecodeValuePastTo490()
+    {
+        // Setup test fixture.
+        final String unencoded = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod";
+        final String base64encoded = "PwwA2Ejt1HDS0xwbEg4qMzk/E9fDA1aA6TdL2zBPMVtwW9C2UnUafAmm/twRZxY89euheVg0rxoQVfo5to825asMcx/bJNPY136oZstULDU=";
+
+        // Execute system under test.
+        final AesEncryptor encryptor = new AesEncryptor();
+        final String result = encryptor.decrypt(base64encoded);
+
+        // Verify results.
+        assertEquals(unencoded, result);
+    }
 }