<%@Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
       CodeBehind="Default.aspx.cs" Inherits="WebApplication1._Default"%>
...
   <asp:TextBox ID="tbxEmail" runat="server"></asp:TextBox>
   <asp:Button ID="btnJoin" runat="server" Text="Join" onclick="btnJoin_Click" />
   <asp:Label ID="lblMessage" runat="server" Text=""></asp:Label>
...

<%@Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
       CodeBehind="Default.aspx.cs" Inherits="WebApplication1._Default"%>
...
   <asp:TextBox ID="tbxEmail" runat="server"></asp:TextBox>
   <asp:Button ID="btnJoin" runat="server" Text="Join" onclick="btnJoin_Click" />
   <asp:Label ID="lblMessage" runat="server" Text=""></asp:Label>
...

public partial class _Default : System.Web.UI.Page
{
   protected void Page_Load(object sender, EventArgs e)
   {
        ...
   }

   protected void btnJoin_Click(object sender, EventArgs e)
   {
       try
       {
           Contact contact = new Contact();
           // Don't care about the id value
           contact.Id = 1;
           contact.EmailAddresses.Add(new EmailAddress() {
                EmailAddr = tbxEmail.Text,
                ConfirmStatus = ConfirmStatus.NoConfirmationRequired,
                Status = Status.Active });
           contact.Lists.Add(new ContactList() {
                Id = 1,
                Status = Status.Active });

           ConstantContact cc = new ConstantContact();
           cc.AddContact(contact);
           lblMessage.Text = "You have been added to my mailing list!";
       }
       catch (Exception ex) { lblMessage.Text = ex.ToString(); }
   }
}

public partial class _Default : System.Web.UI.Page
{
   protected void Page_Load(object sender, EventArgs e)
   {
        ...
   }

   protected void btnJoin_Click(object sender, EventArgs e)
   {
       try
       {
           Contact contact = new Contact();
           // Don't care about the id value
           contact.Id = 1;
           contact.EmailAddresses.Add(new EmailAddress() {
                EmailAddr = tbxEmail.Text,
                ConfirmStatus = ConfirmStatus.NoConfirmationRequired,
                Status = Status.Active });
           contact.Lists.Add(new ContactList() {
                Id = 1,
                Status = Status.Active });

           ConstantContact cc = new ConstantContact();
           cc.AddContact(contact);
           lblMessage.Text = "You have been added to my mailing list!";
       }
       catch (Exception ex) { lblMessage.Text = ex.ToString(); }
   }
}

...
<appSettings>
    <add key="APIKey" value="APIKey"/>
    <add key="Password" value="password"/>
    <add key="Username" value="username"/>
    <add key="RedirectURL" value="http://somedomain"/>
</appSettings>
...

...
<appSettings>
    <add key="APIKey" value="APIKey"/>
    <add key="Password" value="password"/>
    <add key="Username" value="username"/>
    <add key="RedirectURL" value="http://somedomain"/>
</appSettings>
...