Note: This topic applies to ASP.NET Core 2.x
ASP.NET Core ships with support for authenticator applications for individual authentication. Two factor authentication (2FA) authenticator apps, using a Time-based One-time Password Algorithm (TOTP), are the industry recommended approach for 2FA. 2FA using TOTP is preferred to SMS 2FA. An authenticator app provides a 6 to 8 digit code which users must enter after confirming their username and password. Typically an authenticator app is installed on a smart phone.
The ASP.NET Core web app templates support authenticators, but don’t provide support for QRCode generation. QRCode generators ease the setup of 2FA. This document will guide you through adding QR Code generation to the 2FA configuration page.
Adding QR Codes to the 2FA configuration page
These instructions use qrcode.js from the https://davidshimjs.github.io/qrcodejs/ repo.
wwwrootlibfolder in your project.
In PagesAccountManageEnableAuthenticator.cshtml (Razor Pages) or ViewsManageEnableAuthenticator.cshtml (MVC), locate the
Scriptssection at the end of the file:
@section Scripts @await Html.PartialAsync("_ValidationScriptsPartial")
- Update the
Scriptssection to add a reference to the
qrcodejslibrary you added and a call to generate the QR Code. It should look as follows:
- Delete the paragraph which links you to these instructions.
Run your app and ensure that you can scan the QR code and validate the code the authenticator proves.
Change the site name in the QR Code
The site name in the QR Code is taken from the project name you choose when initially creating your project. You can change it by looking for the
GenerateQrCodeUri(string email, string unformattedKey) method in the PagesAccountManageEnableAuthenticator.cshtml.cs (Razor Pages) file or the ControllersManageController.cs (MVC) file.
The default code from the template looks as follows:
private string GenerateQrCodeUri(string email, string unformattedKey) return string.Format( AuthenicatorUriFormat, _urlEncoder.Encode("Razor Pages"), _urlEncoder.Encode(email), unformattedKey);
The second parameter in the call to
string.Format is your site name, taken from your solution name. It can be changed to any value, but it must always be URL encoded.
Using a different QR Code library
You can replace the QR Code library with your preferred library. The HTML contains a
qrCode element into which you can place a QR Code by whatever mechanism your library provides.
The correctly formatted URL for the QR Code is available in the:
AuthenticatorUriproperty of the model.
data-urlproperty in the
TOTP client and server time skew
TOTP (Time-based One-Time Password) authentication depends on both the server and authenticator device having an accurate time. Tokens only last for 30 seconds. If TOTP 2FA logins are failing, check that the server time is accurate, and preferably synchronized to an accurate NTP service.