OTP in dotnet identity

Data

TwoFactorenabled and TwoFactorDefined fields of the user should be false in AspNetUser Table

Creating Authenticator App Entry

Code

        public async Task<string> GetAuthenticator(string username)
        {
            var user = await userManager.FindByEmailAsync(username);
            var unformattedKey = await userManager.GetAuthenticatorKeyAsync(user);
            if (string.IsNullOrEmpty(unformattedKey))
            {
                await userManager.ResetAuthenticatorKeyAsync(user);
                unformattedKey = await userManager.GetAuthenticatorKeyAsync(user);
            }

            var AuthenticatorUri = GenerateQrCodeUri(user.UserName, unformattedKey);
            return AuthenticatorUri;
        }

        private string GenerateQrCodeUri(string email, string unformattedKey)
        {
            var authenticatorTitle = settingManager.GetSetting("AuthenticatorTitle");
             var  AuthenticatorUriFormat = "otpauth://totp/{0}:{1}?secret={2}&issuer={0}&digits=6";
            return string.Format(
            AuthenticatorUriFormat,
                _urlEncoder.Encode(authenticatorTitle),
                _urlEncoder.Encode(email),
                unformattedKey);
        }

it gives you the link

otpauth://totp/Logicmade:ali.iybar@gmail.com?secret=CKNZWXGDHTQUZYU37S6XYYTOQJAUX6ZE&issuer=Logicmade&digits=6

The link in details

Logicmade: it is an open text. Name of your site

ali.iybar@gmail.com : it's the user email in identity user

secret : it's the code we get from userManager.GetAuthenticatorKeyAsync

Logicmade (issuer) : issuer :)

digits : it's how many digits you need to authenticate

Creating a QR Code

use any QR code generator and put the link in it.

Add link to Authenticator app

Open the authenticator app and click + to add a new one. Select QR code and read the QR code you created above

Validating

just stub the code below to Sign in wherever needed.

var user = await userManager.FindByEmailAsync(userSignIn.Email);
....
var otpResult = await userManager.VerifyTwoFactorTokenAsync(user, TokenOptions.DefaultAuthenticatorProvider, userSignIn.OTP);
if (!otpResult)
{
  throw new Exception("OTP mismatch");
}

userSignIn.OTP : this is the 6 digit code created in the app