GUACAMOLE-362: Deal gracefully with situations where password cannot be decrypted.

extensions/guacamole-auth-cas/src/main/java/org/apache/guacamole/auth/cas/AuthenticationProviderService.java

@@ -173,10 +173,15 @@ public class AuthenticationProviderService {
 
             final Cipher cipher = confService.getClearpassCipher();
 
-            // Decrypt and return a new string.
-            final byte[] pass64 = DatatypeConverter.parseBase64Binary(encryptedPassword);
-            final byte[] cipherData = cipher.doFinal(pass64);
-            return new String(cipherData);
+            if (cipher != null) {
+
+                // Decode and decrypt, and return a new string.
+                final byte[] pass64 = DatatypeConverter.parseBase64Binary(encryptedPassword);
+                final byte[] cipherData = cipher.doFinal(pass64);
+                return new String(cipherData);
+
+            }
+
         }
         catch (Throwable t) {
             logger.error("Failed to decrypt the data, password token will not be available.");
@@ -184,6 +189,9 @@ public class AuthenticationProviderService {
             return null;
         }
 
+        logger.warn("Encrypted password provided by CAS, but no Private Key was available to decrypt it.");
+        return null;
+
     }
 
 }