Form Authentication for Mobile Applications in VB.NET

Introduction.

In this example we will authenticate mobile web users for our application using Forms Authentication.

Other forms of authentication for mobile web applications are

- Windows Authentication.
- Passport Authentication.

Technique.

When the user requests for a mobile web page from the application and if the user is not authenticated, the user is directed to the login page specified in the configuration settings. The user is prompted to enter the login and password. After the user is authenticated and authorized to access the page, the user is sent to the requested page (or the default page of the web site, if none is specifically requested). The user is now free to access the web site and navigate through the web site without being re-prompted for the login information.

When the user is done with the processing, he/she can Signout from the Application.

You can also specify a time-out period for the duration of time after which the validity of the login expires.

Since mobile pages may or may not support cookies, we enable cookieless operation.

Program Details.

Step 1: Create the project:

Create a Visual VB Mobile Web Application in Visual Studio.Net.

Step 2: Create the login Mobile Web Page.

Add a new Mobile Web Form to the project and name the page Login.aspx
Add the controls as shown in figure 1 below.

FormAuthInWebImg1-in-vb.net.gif

Figure 1: Login.aspx.

Change the following properties for controls added on the mobile web page:

Control	Property	Value
Label	Text	Login:
TextBox	Id	txtLogin
Label	Text	Password
Textbox	Id	txtPwd
	Password	True
Command	Id	Login
	Id	cmdLogin
Label	Id	lblError

Double click on the Command Control to start adding code to event handler for the onClick Event.

Add the following code to the OnClick event handler of the Command control.

FormsAuthentication.Authenticate(txtLogin.Text, txtPwd.Text) Then
FormsAuthentication.SetAuthCookie(txtLogin.Text, False)
MobileFormsAuthentication.RedirectFromLoginPage(txtLogin.Text, True)
Else
lblError.Text = "Please check your credentials"
End If

This is the code where the actual authentication occurs. If the user cannot be authenticated in the system, then we display and error message and prevent the user from proceeding in the site.

If the user is authenticated successfully, the user is directed to the requested page.

Add the following line of code to the top of the mobile web page.

Imports System.Web.Security.

Step 3: Create the other pages in the web site.

We can now create the rest of the web site. Since this example is used to demonstrate forms authentication, our site will only contain two mobile web pages. Open the default web form that was created in the project "MobileWebForm1.aspx" and add a label control, a link control and a Command control. Change the properties of the control as shown in the table below.

Control	Property	Value
Label1	Text	Home Page
Link	Text	Go To Mobile Web Page 2
	NavigateURL	MobileWebForm2.aspx
Command	Text	Logout
	Id	cmdLogout
Form

Rename the mobile web page "default.aspx"

Add the following code to the OnClick event handler of the Command control.

MobileFormsAuthentication.SignOut()
RedirectToMobilePage("login.aspx", True)

Now add another Mobile Web Page in the project. Add a label and a link control on the mobile web form on this web page and set the following properties :

Control	Property	Value
Label	Text	Mobile Web Page 2.
Link	Text	Back To HomePage.
	NavigateURL	defaul.aspx.

Step 4: Modify the configuration Settings.

This is the main part where we specify that we opt for Forms Authentication.

Add the following changes to the web.config file included in the project:

Delete the section for authentication in the existing file and add the following instead:

authentication mode="Forms" >
<forms loginUrl="login.aspx" name=".COOKIEDEMO" timeout="60" path="/" >
<credentials passwordFormat="SHA1">
<user name="user1"
password=" 5BAA61E4C9B93F3F0682250B6CF8331B7EE68FD8"/>
<user name="user2"
password=" 5BAA61E4C9B93F3F0682250B6CF8331B7EE68FD8"/>
</credentials>
</forms>
</authentication>
<authorization>
<deny users="?" />
</authorization>

This section specifies the use of forms authentication and provides the passwords for the users using format "SHA1". In this example the password for both the users is set to "password". The trick in deriving the encoded value of password is making use of the function:

FormsAuthentication.HashPasswordForStoringInConfigFile.

We have also indicated in the <authorization> section that anonymous users must be denied access to all files in this application.

Replace the existing section for the SessionState with the following.

sessionState cookieless="true"/>

Step 5: Build and Run the program and see the results.

When you initially request for the mobile web page belonging to this application, you are not authenticated and hence, directed to the login page.

FormAuthInWebImg2-in-vb.net.gif

Figure 2: In the initial request, the user is not authenticated and therefore, directed to the Login Web page.

Enter the following credentials:

Login: user1
Password: password

Note that the password text is not displayed to the user.

Click on the Login button and you will be sent to the requested web site if the correct credentials are entered.

FormAuthInWebImg3-in-vb.net.gif

Figure 3: User is authenticated successfully and redirected to the requested page.

After this the user will have access to the other web pages in the web site and won't be prompted for login unless the Logout button is clicked or the validity of the login expires.

If the user clicks on the Logout button, he/she is logged out and redirected to the login page.

FormAuthInWebImg4-in-vb.net.gif

Figure 4: Incorrect Credentials-Note the error message.

Conclusion:

Security is a major concern for all applications, especially for Mobile Web Applications. We saw the use of FormsAuthentication in this example. Forms Authentication does not depend on IIS. You can build on this simple example and fortify your web site against invalid access.