OF-1381 Close SCRAM enumeration attack

getIterations() threw an exception which
caused early termination of the SASL exchange.

Spotted by Phil Roberts of Surevine Ltd.

src/java/org/jivesoftware/openfire/sasl/ScramSha1SaslServer.java

@@ -35,6 +35,7 @@ import org.jivesoftware.openfire.auth.ConnectionException;
 import org.jivesoftware.openfire.auth.InternalUnauthenticatedException;
 import org.jivesoftware.openfire.auth.ScramUtils;
 import org.jivesoftware.openfire.user.UserNotFoundException;
+import org.jivesoftware.util.JiveGlobals;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -149,13 +150,8 @@ public class ScramSha1SaslServer implements SaslServer {
         String clientNonce = m.group(7);
         nonce = clientNonce + UUID.randomUUID().toString();
 
-        try {
         serverFirstMessage = String.format("r=%s,s=%s,i=%d", nonce, DatatypeConverter.printBase64Binary(getSalt(username)),
                 getIterations(username));
-		} catch (UserNotFoundException e) {
-            throw new SaslException(e.getMessage(), e);
-		}
-        
         return serverFirstMessage.getBytes(StandardCharsets.UTF_8);
     }
 
@@ -332,8 +328,13 @@ public class ScramSha1SaslServer implements SaslServer {
     /**
      * Retrieve the iteration count from the database for a given username.
      */
-    private int getIterations(final String username) throws UserNotFoundException {
+    private int getIterations(final String username) {
+        try {
             return AuthFactory.getIterations(username);
+        } catch (UserNotFoundException e) {
+            return JiveGlobals.getIntProperty("sasl.scram-sha-1.iteration-count",
+                ScramUtils.DEFAULT_ITERATION_COUNT);
+        }
     }
     
     /**