Fix issue jaredhanson#180

Author: relativityboy

lib/strategy.js

@@ -68,10 +68,17 @@ util.inherits(Strategy, passport.Strategy);
  */
 Strategy.prototype.authenticate = function(req, options) {
   options = options || {};
-  var username = lookup(req.body, this._usernameField) || lookup(req.query, this._usernameField);
-  var password = lookup(req.body, this._passwordField) || lookup(req.query, this._passwordField);
+  var username = lookup(req.body, this._usernameField) 
+  if(username === null) {
+    lookup(req.query, this._usernameField);
+  }
+  
+  var password = lookup(req.body, this._passwordField) 
+  if(password === null) {
+    password = lookup(req.query, this._passwordField);
+  }
 
-  if (!username || !password) {
+  if (username === null || password === null) {
     return this.fail({ message: options.badRequestMessage || 'Missing credentials' }, 400);
   }