ASP.NET: Using Forms Authentication in ASP.NET


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There are times when you want to validate users hitting a web site on your own rather than using Windows or Passport authentication. That requires forms based security. This article shows you how to implement Forms Based Authentication.

Hitting any web page on the site will automatically redirect to the login form. When the login form has authenticated the user, it will automatically redirect back to the originally requested page. Failure to log in will prohibit the user from hitting the originally requested page.

Each example below is shown in both Visual Basic .NET and C#. Use the appropriate code for the language you are using.

In the web.config file in the root of the web site, insert this XML:

<authentication mode="Forms">
    <forms name="login" loginUrl="login.aspx" />
</authentication>

<authorization>
    <allow roles="bigboss" />
    <allow roles="wimpyuser" />
    <allow users="admin" />
    <deny users="*" />
</authorization>

Change the rules to give permissions to the proper users and roles. You may create a different web.config and its authorization section in each subdirectory with different rules.

In the global.asax file, insert this code:

[vb.net]
Imports System.Security.Principal
Imports System.Web.Security

Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
    ' Fires upon attempting to authenticate the use
    If Not (HttpContext.Current.User Is Nothing) Then
        If HttpContext.Current.User.Identity.IsAuthenticated Then
            If TypeOf HttpContext.Current.User.Identity Is FormsIdentity Then
                Dim fi As FormsIdentity = CType(HttpContext.Current.User.Identity, FormsIdentity)
                Dim fat As FormsAuthenticationTicket = fi.Ticket

                Dim astrRoles As String() = fat.UserData.Split("|"c)
                HttpContext.Current.User = New GenericPrincipal(fi, astrRoles)
            End If
        End If
    End If
End Sub

[c#]
using System.Security.Principal;
using System.Web.Security;

protected void Application_AuthenticateRequest(Object sender, EventArgs e)
{
	//Fires upon attempting to authenticate the use
	if (!(HttpContext.Current.User == null))
	{
		if (HttpContext.Current.User.Identity.IsAuthenticated)
		{
			if (HttpContext.Current.User.Identity.GetType() == typeof(FormsIdentity))
			{
				FormsIdentity fi = (FormsIdentity) HttpContext.Current.User.Identity;
				FormsAuthenticationTicket fat = fi.Ticket;

				String[] astrRoles = fat.UserData.Split('|');
				HttpContext.Current.User = new GenericPrincipal(fi, astrRoles);
			}
		}
	}
}

Create a Web Form named login.aspx, set the style to Flow Layout, and put this onto the page:

<table height="66%" width="100%">
    <tr>
        <td align="middle">
            <table id="loginbox" width="300" class="itemstyle">
                <tr>
                    <td id="login" align="middle" colspan="3">Login</td>
                </tr>
                <tr>
                    <td>Username:</td>
                    <td><asp:textbox id="txtUsername" tabindex="4" runat="server" 
                    columns="12"></asp:textbox></td>
                    <td valign="center" align="middle" rowspan="2">
                        <asp:button id="btnLogin" runat="server" text="Login" 
                        cssclass="button"></asp:button></td>
                <tr>
                    <td>Password:</td>
                    <td><asp:textbox id="txtPassword" runat="server" columns="12" 
                    textmode="Password"></asp:textbox></td>
                </tr>
                <tr>
                    <td>&nbsp;</td>
                    <td colspan="2"><asp:label id="lblError" runat="server" 
                    forecolor="Red" visible="False">Not a valid username or password.</asp:label>
                    </td>
                </tr>
            </table>
        </td>
    </tr>
</table>

In the CodeBehind for login.aspx, put this code:

[vb.net]
Imports System.Web.Security

Private Sub btnLogin_Click(ByVal sender As Object, ByVal e As System.EventArgs) _
 Handles btnLogin.Click
    If ValidateUser(txtUsername.Text, txtPassword.Text) Then
        FormsAuthentication.Initialize()
        Dim strRole As String = AssignRoles(txtUsername.Text)

        'The AddMinutes determines how long the user will be logged in after leaving
        'the site if he doesn't log off.
        Dim fat As FormsAuthenticationTicket = New FormsAuthenticationTicket(1, _
         txtUsername.Text, DateTime.Now, _
         DateTime.Now.AddMinutes(30), False, strRole, _
         FormsAuthentication.FormsCookiePath)
        Response.Cookies.Add(New HttpCookie(FormsAuthentication.FormsCookieName, _
         FormsAuthentication.Encrypt(fat)))
        Response.Redirect(FormsAuthentication.GetRedirectUrl(txtUsername.Text, False))
    Else
        lblError.Visible = True
    End If
End Sub

Private Function ValidateUser(ByVal strUsername As String, ByVal strPassword As String) _
 As Boolean
    'Return true if the username and password is valid, false if it isn't
    Return CBool(strUsername = "admin" AndAlso strPassword = "password")
End Function

Private Function AssignRoles(ByVal strUsername As String) As String
    'Return a | separated list of roles this user is a member of
    If txtUsername.Text = "admin" Then
        Return "bigboss|wimpyuser"
    Else
        Return String.Empty
    End If
End Function

[c#]
using System.Web.Security;

private void btnLogin_Click(object sender, System.EventArgs e)
{
	if (ValidateUser(txtUsername.Text, txtPassword.Text))
	{
		FormsAuthentication.Initialize();
		String strRole = AssignRoles(txtUsername.Text);

		//The AddMinutes determines how long the user will be logged in after leaving
		//the site if he doesn't log off.
		FormsAuthenticationTicket fat = new FormsAuthenticationTicket(1, 
			txtUsername.Text, DateTime.Now, 
			DateTime.Now.AddMinutes(30), false, strRole, 
			FormsAuthentication.FormsCookiePath);
		Response.Cookies.Add(new HttpCookie(FormsAuthentication.FormsCookieName, 
			FormsAuthentication.Encrypt(fat)));
		Response.Redirect(FormsAuthentication.GetRedirectUrl(txtUsername.Text, false));
	}
	else
		lblError.Visible = true;
}

private Boolean ValidateUser(String strUsername, String strPassword)
{
   //Return true if the username and password is valid, false if it isn't
	return ((strUsername == "admin") && (strPassword == "password"));
}

private String AssignRoles(String strUsername)
{
	//Return a | separated list of roles this user is a member of
	if (txtUsername.Text == "admin")
		return "bigboss|wimpyuser";
	else
		return String.Empty;
}

Change the ValidateUser and AssignRoles to do lookups into a database or other data store instead of the hardcoded validation and role assignment shown.

On each page on the site, you will need a way to log out. Simply put a hyperlink to the logout page:

<asp:HyperLink id="hlLogout" runat="server" 
NavigateUrl="logout.aspx">Logout</asp:HyperLink>

The logout.aspx page should have this on it:

<table width="100%">
    <tr>
        <td align="middle">
            You have been logged out.
            <asp:hyperlink id="hlLogin" runat="server" 
            navigateurl="default.aspx">Log back in.</asp:hyperlink>
        </td>
    </tr>
</table>

The CodeBehind for the logout page should include this:

[vb.net]
Imports System.Web.Security

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) _
 Handles MyBase.Load
    Session.Abandon()
    FormsAuthentication.SignOut()
End Sub

[c#]
using System.Web.Security;

private void Page_Load(object sender, System.EventArgs e)
{
	// Put user code to initialize the page here
	Session.Abandon();
	FormsAuthentication.SignOut();
}

You can put things that are only allowable to certain roles on your web page by using code like this:

[vb.net]
hlAdmin.Visible = Page.User.IsInRole("bigboss")

[c#]
hlAdmin.Visible = Page.User.IsInRole("bigboss");

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