In this article, we are going to learn how to perform two-factor authentication in an ASP.NET Core application using Google Authenticator app. The user needs to configure the Google Authenticator app on his/her smartphone using the QR code generated in the web app. At the time of logging in to the web application, a user has to enter a six-digit pin that will be generated in the app to finish two-factor authentication. The key generated in the app will be unique to the userid and is a time-based one-time password (TOTP); i.e., it will expire after a certain time.
- Install .NET Core 2.0.0 or above SDK from here.
- Install the latest version of Visual Studio 2017 Community Edition from here.
Before proceeding I would recommend you to get the source code from Github
Create MVC Web Application
Open Visual Studio and select File >> New >> Project. After selecting the project, a “New Project” dialog will open. Select .NET Core inside Visual C# menu from the left panel. Then, select “ASP.NET Core Web Application” from available project types. Put the name of the project as TwoFactAuth and press OK.
After clicking OK, a new dialog will open asking you to select the project template. You can observe two drop-down menus at the top left of the template window. Select “.NET Core” and “ASP.NET Core 2.0” from these drop-downs. Then, select “Web application (Model-View-Controller)” template. Click on “Change Authentication” button; a “Change Authentication” dialog box will open. Select “Individual User Account” and click OK. Now, click OK again to create our web app.
Adding QR Codes to configure two-factor authentication
Open Views\Manage\EnableAuthenticator.cshtml file. You will find @section Scripts at the end of the file. Put the following code in it.
This EnableAuthenticator.cshtml file already have a div with id “qrCode” (see line 25 in below code). We are generating a QR code inside that div using qrcode.js library. We are also defining the dimensions of the QR code in form of width and height.
So finally, your EnableAuthenticator.cshtml file will look like this.
When we execute the program, a QR code will be generated in this View and the user can set up two factor authentication using the Google authenticator with the help of this QR code.
Configure two-factor authentication
Before running the application, we need to apply migrations to our app. Navigate to Tools >> NuGet Package Manager >> Package Manager Console. It will open the Package Manager Console. Put in Update-Database command and hit Enter. This will update the database using Entity Framework Code First Migrations.
Press F5 to launch the application and click on Register in the top right corner of the homepage. You can see a user registration page. Fill in the details and click on Register button as shown in the image below.
Upon successful registration, you will be logged into the application and navigated to the home page. Here, you can see your registered Email id at the top right corner of the page. Click on it to navigate to “Manage your account” page. Select TwoFactorAuthentication from the left menu. You can see a page similar to that shown below.
Click on Configure authenticator app button. You can see a QR code generated on your screen and it is asking for a Verification Code also as shown in the image below.
You need to install Google Authenticator app on your smartphone to scan this QR code in order to generate a Verification Code and complete two-factor authentication setup. Download and install Google authenticator for Android from Play Store and for iOS from App Store. I am using an Android device for this demo.
Launch the app on your smartphone. You can see the welcome screen as shown in the image below.
- Scan a barcode
- Enter a provided key
Click on “Scan a barcode” and scan the QR code generated by the web app. This will add a new account to Google authenticator and generate a six-digit pin on your mobile screen. This is our two-factor authentication code. This is a TOTP ( time-based one-time password). You can observe that it keeps on changing frequently (life span of 30 seconds).
And thus, the two-factor authentication setup is complete. Let’s check if our two-factor authentication is working correctly or not.
Logout of the application and click on login again. Enter your registered email id and password and click on login.
Now you can see a the two-factor authentication screen asking for Authenticator code. Put in the code that is generated currently in your Google Authenticator app and click on Login. You will be successfully logged into the application and navigated to the home page.
If you check “Remember this machine” option then it will not ask for Authenticator code on the same machine again. You can skip the two-factor authentication in this case.
You can also find this article at C# Corner.
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