用EXTJS前台做登录验证。

如题前台用EXTJS 做了个登录框，
后台用什么事件触发事件来获取前台的输入数据 后验证用户名和密码正确了后返回
部分代码
login.aspx
<head runat="server">
    <title>登录</title>
    <link rel="stylesheet" type="text/css" href="extjs/resources/css/ext-all.css" />
    <script  type="text/javascript" src="extjs/adapter/ext/ext-base.js"></script>
    <script type="text/javascript" src="extjs/ext-all.js"></script>
    <script type="text/javascript" src="JS/login.js"></script>   
</head>
<body>
    <form id="form1" runat="server">
    <div id="yes">
   
    </div>
    </form>
</body>
login.js文件这样
Ext.onReady(function(){
    Ext.QuickTips.init();//初始化全局 QuickTips 实例.设置当出错时提示信息
    Ext.form.Field.prototype.msgTarget = 'side';//初始化提示标志.设置当出错时提示标志的感叹号图标 
    var login = new Ext.FormPanel({ //Panel：面板
        title:"登 陆",
        frame:true,        //属性frame：把四个角变成圆角        
        width:260,
        height:130,
        layout:"form",
        labelWidth:45,
        defaults:{xtype:"textfield",width:180},
        items:[{      //items：指定包含在面板中的组件的配置数组
            fieldLabel:"账 号",
            name:"uName",
            allowBlank:false
        },{
            fieldLabel:"密 码",
            name:"uPsw",
            inputType:"password",
            allowBlank:false
        }],
    buttons:[{   
                text:'Login',  
                formBind: true,    
                // Function that fires when user clicks the button   
                handler:function(){   
                    login.getForm().submit({   
                         method:'POST', 
                         url:'login.aspx',  
                         waitTitle:'Connecting',   
                         waitMsg:'Sending data...',  
   
            // Functions that fire (success or failure) when the server responds.   
            // The one that executes is determined by the   
            // response that comes from login.asp as seen below. The server would   
            // actually respond with valid JSON,   
            // something like: response.write "{ success: true}" or   
            // response.write "{ success: false, errors: { reason: 'Login failed. Try again.' }}"   
            // depending on the logic contained within your server script.  
            // If a success occurs, the user is notified with an alert messagebox,   
            // and when they click "OK", they are redirected to whatever page  
            // you define as redirect.   
    
                       success:function(){   
                            Ext.Msg.alert('Status', 'Login Successful!', function(btn, text){  
                                if (btn == 'ok'){  
                                   var redirect = 'index.aspx';   
                                   window.location = redirect;  
                                   }  
                    });  
                       },  
   
            // Failure function, see comment above re: success and failure.   
            // 如果登录失败，弹出对话框。   
   
                       failure:function(form, action){   
                            if(action.failureType == 'server'){   
                                 obj = Ext.util.JSON.decode(action.response.responseText);   
                                Ext.Msg.alert('Login Failed!', obj.errors.reason);   
                            }else{   
                                Ext.Msg.alert('Warning!', 'Authentication server is unreachable : ' + action.response.responseText);   
                           }   
                            login.getForm().reset();   
                         }   
                    });   
                 }   
            },
            {
                text:'Cancel',
                formBind:true,
                handler:function(){login.getForm().reset();}
            }]
    });
    var win = new Ext.Window({  
         layout:'fit',  
          width:300,  
         height:150,  
         closable: false,  
         resizable: false,  
         plain: true,  
          items: [login]  
      });  
     win.show();
   
   
});
  后台login.aspx.cs 该怎么写啊 关键是 用什么事件触发 
如果用page_load 事件和request方法来获取输入的用户名和密码 
在页面加载时 还没输入数据啊 怎么得到数据啊