关于httpclient模拟post的问题

aspx页面的一个form 通过 点击 登录 按钮 获得一个在text输入的账号和密码后，调用on_click事件来验证，再返回登录结果。
我现在想 如何才能激发这个on_click事件 多谢了
   <form id="form1" runat="server">
   
    <div id="content"><!--内容-->
       <div id="left"> </div>   
       <div id="midline"></div>
       <div id="right"><!--右边 登陆表单-->
       <div id="menu">
          <img src="images/signup.png" class="entrance"/>
         <span class="userbg">
                <asp:TextBox ID="nickname"  CssClass="nickname" runat="server"  value="test"/>
                <asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" 
                    ControlToValidate="nickname" ErrorMessage="*用户名必填*" 
               CssClass="errormsg1" Height="23px" Width="241px" />   
           </span>   
          <span class="pwbg">
            <asp:TextBox ID="password" runat="server" TextMode="Password" CssClass="password" value="test"></asp:TextBox>
            <asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" 
            ControlToValidate="password" ErrorMessage="密码必填" CssClass="errormsg2" /> </span>
            <asp:Button ID="Button1" runat="server" Text="登 陆"  onclick="Button1_Click" class="button" />
            <input type="button" value="注 册" onclick="javascript:document.location='register.aspx';" class="button register" />              </form>
下面是button1_Click事件：
protected void Button1_Click(object sender, EventArgs e)
    {        if (this.nickname.Text == "" || this.password.Text == "")
        {
            Common.ShowMsg("请填写完整！");
        }
        else
        {            string nick = this.nickname.Text;
            string pwd = System.Web.Security.FormsAuthentication.HashPasswordForStoringInConfigFile(this.password.Text, "MD5");
                Student s = this.sbll.loginStudent(nick, pwd);
                if (s != null)
                {
                    Session.Add("student", s);
                    Response.Redirect("Student/Default.html");
                }
                else
                {
                    Response.Write("<script>alert('用户名或密码不存在');history.back();</script>");
                  //  Response.Redirect("default.aspx");
                }        }
    }