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.NET Core C# Two-factor Authentication Quickstart

As of November 2022, Twilio no longer provides support for Authy SMS/Voice-only customers. Customers who were also using Authy TOTP or Push prior to March 1, 2023 are still supported. The Authy API is now closed to new customers and will be fully deprecated in the future.

For new development, we encourage you to use the Verify v2 API.

Existing customers will not be impacted at this time until Authy API has reached End of Life. For more information about migration, see Migrating from Authy to Verify for SMS.

Adding two-factor authentication to your application is the easiest way to increase security and trust in your product without unnecessarily burdening your users. This quickstart guides you through building an ASP.NET Core, AngularJS, and SQL Server application that restricts access to a URL. Four Authy API channels are demoed: SMS, Voice, Soft Tokens and Push Notifications.

Ready to protect your toy app's users from nefarious balaclava wearing hackers? Dive in!

Sign Into - or Sign Up For - a Twilio Account

Create a new Twilio account (you can sign up for a free Twilio trial), or sign into an existing Twilio account.

Create a New Authy Application

Once logged in, visit the Authy Console. Click on the red 'Create New Aplication' (or big red plus ('+') if you already created one) to create a new Authy application then name it something memorable.

Authy create new application

You'll automatically be transported to the Settings page next. Click the eyeball icon to reveal your Production API Key.

Account Security API Key

Copy your Production API Key to a safe place, you will use it during application setup.

Setup Authy on Your Device

This two-factor authentication demos two channels which require an installed Authy app to test: Soft tokens and push authentications. While SMS and voice channels will work without the client, to try out all four authentication channels download and install the Authy app for Desktop or Mobile:

Clone and Setup the Application

Start by cloning our repository. Then, enter the directory and install dependencies:

git clone
cd account-security-csharp/src/AccountSecurity
dotnet restore

Next, open the file appsettings.json. There, edit the AuthyApiKey, pasting in the API Key from the above step (in the console), and save.

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        Enter the API Key from the Account Security console.

        Add Your Application API Key

        Enter the API Key from the Account Security console.

        Install and Launch SQL Server

        When a user registers with your application, a request is made to Twilio to add that user to your App, and a user_id is returned. In this demo, we'll store the returned user_id in an MSSQL database.

        On Windows, you can install the free SQL Server Express:

        On Linux or Mac, run it as a docker container:

        docker run -e 'ACCEPT_EULA=Y' -e 'SA_PASSWORD=yourStrong(!)Password' \
        -p 1433:1433 --name mssql -d microsoft/mssql-server-linux:latest​

        Make sure your DefaultConnection connection string in appsettings.json is correct for your SQL Server installation. You may need to change the Server to localhost\\SQLEXPRESS if running MSSQL Server Express on Windows. Or, you may need to change the password if you selected a different one when starting your Docker container.

        Run the database migrations:

        dotnet ef database update -v

        Once you have added your API Key, you are ready to run! Run the app with:

        dotnet run --environment development

        Try the .NET Core C# Two-Factor Demo

        With your phone (optionally with the Authy client installed) nearby, open a new browser tab and navigate to https://localhost:5001/register/

        Enter your information and invent a password, then hit 'Register'. Your information is passed to Twilio (you will be able to see your user immediately in the console), and the application is returned a user_id.

        Now visit https://localhost:5001/login/ and login. You'll be presented with a happy screen:

        Token Verification Page

        If your phone has the Authy app installed, you can immediately enter a soft token from the client to Verify. Additionally, you can try a push authentication simply by pushing the labeled button.

        If you do not have the Authy app installed, the SMS and voice channels will also work in providing a token. To try different channels, you can logout to start the process again.

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              Two Factor Authentication Channels

              And there you go, two-factor authentication is on and your .NET Core C# App is protected!

              What's Next?

              Now that you are keeping the hackers out of this demo app using two-factor authentication, you can find all of the detailed descriptions for options and API calls in our Authy API Reference. If you're also building a registration flow, also check out our Twilio Verify product and the Verification Quickstart which uses this codebase.

              For additional guides and tutorials on account security and other products, in C# and in other languages, take a look at the Docs.

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              Need some help?

              We all do sometimes; code is hard. Get help now from our support team, or lean on the wisdom of the crowd by visiting Twilio's Stack Overflow Collective or browsing the Twilio tag on Stack Overflow.

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