ESET Secure Authentication SDK Developer Guide

.NET SDK

Introduction

The ESET Secure Authentication SDK allows two-factor authentication to be added to any system implemented using the .NET Framework.

This document describes how to use the SDK to provision a user for text message OTPs and how to authenticate OTPs. The document includes C# code snippets.

Using the SDK

The entire SDK is encapsulated in a single .NET 3.5 library. The "ESET.SecureAuthentication.SDK" package must be installed from NuGet, which will manage the required dependencies. The "ESET.SecureAuthentication.SDK" library must be referenced in your Visual Studio project.

The SDK can be installed via NuGet as follows:

1. Add the following NuGet package source from within Visual Studio:
   • Name: ESET Secure Authentication
   • Source: https://esa.eset.com/sdk/packages/nuget
2. Install the "ESET.SecureAuthentication.SDK" package into the appropriate project(s)

Creating an Authenticator Instance

The TwoFactorAuthenticator class is the entry point into the SDK and is used to get users and authenticate OTPs for users.

The TwoFactorAuthenticator integrates with your existing user database via the IUserStorage interface. The two-factor user data will be stored in your database as a string for each user. Add this string as a new column called "esa_data" to your users table. You must implement the IUserStorage interface in order to instantiate the TwoFactorAuthenticator class. The following C# snippet gives an example of how to implement the interface:

public class CustomUserStorage : IUserStorage
{
    // implement by returning the string in the "esa_data" field for the user
    public string LoadUser(string username)
    {
        throw new NotImplementedException();
    }

    // implement by saving the "data" string into the "esa_data" field for the user
    public void SaveUser(string username, string data)
    {
        throw new NotImplementedException();
    }
}

The TwoFactorAuthenticator requires an instance of the TwoFactorConfiguration class. The TwoFactorConfiguration class requires your SDK credentials (API key and shared secret) and an instance of your implementation of IUserStorage (eg the CustomUserStorage class from the above snippet). The following C# snippet illustrates this:

// create an instance of your implementation of IUserStorage
IUserStorage userStorage = new CustomUserStorage();

// replace with your credentials
const string apiKey = "KEY";
const string apiSecret = "SECRET";

// create configuration object
var configuration = new TwoFactorConfiguration(apiKey, apiSecret, userStorage);

// create authenticator instance
var authenticator = new TwoFactorAuthenticator(configuration);

The authenticator instance can now be used to provision and authenticate users.

Provision a User for Text Message OTPs

Once a user is provisioned for text message OTPs, they will be sent an OTP via text message during each authentication attempt.

The username and mobile number are required to provision a user for text message OTPs.

Note: Mobile numbers must be in the format '42612345678', where '4' is the country code and '26' is the area code.

The following C# snippets details this:

const string username = "user1";
const string mobileNumber = "42612345678";

using (TwoFactorUser twoFactorUser = authenticator.CreateUser(username, mobileNumber))
{
    twoFactorUser.ProvisionTextMessage();
}

The TwoFactorUser class implements IDisposable and must be disposed (such as in a "using" statement) after use for any changes to be persisted.

User Authentication

The authentication process consists of two steps.

The first step is the pre-authentication step. This step will send a text message OTP to the user:

// start the authentication process, which will send a text message OTP to the user
authenticator.PreAuthenticate(username);

The second step authenticates an OTP entered by the user. The result from this step will indicate if authentication succeeded or not. The following C# snippet details this:

// this value must be captured from the user
string otp = "123456";

// authenticate an OTP entered by the user
AuthenticateResult authenticateResult = authenticator.Authenticate(username, otp);

if (authenticateResult.IsAuthenticated)
{
    // the authentication has succeeded, the user may be logged in
}
else
{
    // the authentication has failed
}

Details

User Details

The TwoFactorUser class exposes the following properties:

• IsLocked – specifies if the user has been locked due to too many failed authentication attempts. Locked users cannot be authenticated

The TwoFactorUser class exposes the following methods:

• ProvisionTextMessage – provisions the user for text message OTPs
• ProvisionMobileApp – provisions the user for mobile app OTPs. The return value contains the mobile app installation URL. This method does not automatically send the URL via text message to the user
• SendMobileAppProvisioningTextMessage – send mobile app installation URL to user via text message. This method accepts the result from ProvisionMobileApp as an input parameter
• Unlock – unlocks a locked user
• DeProvision – disables two-factor authentication for a user. This decrements your license's active user count

Provisioning users for text message OTPs or mobile app OTPs increments your license's active user count.

Configuration Details

Default configuration can be overridden by setting the following properties on the TwoFactorConfiguration class:

• TokenName – the name of the token displayed in the user's mobile app (defaults to "SDK Token")
• PINEnforced – if enabled, all users must protect their mobile app with a PIN
• AppInstallTextMessageText – the text that will be displayed in the text message containing the mobile app installation URL. The text must contain the "__ESA_APP_INSTALL_URL__" placeholder string
• TextMessageOTPText – the text that will be displayed when text message OTPs are sent. The text must contain the "__ESA_SMS_OTP__" placeholder string
• MaxFailuresBeforeLocking – the number of failed authentication attempts allowed before the user is locked. The value must be in the range of 3-30 (inclusive)
• TextMessageOTPLifetime – the number of minutes before a text message OTP expires. The value must be in the range of 5-60 (inclusive)

Pre-authentication Detail

The pre-authenticate method returns a PreAuthenticateResult object. The result includes an ExpectedCredential property (of enum type CredentialTypes) that indicates the type of OTP that is to be expected.

The CredentialTypes enum has the following values:

• None – the user is not enabled for two-factor authentication
• TextMessageCredential – the user is enabled for text message OTPs
• AppHOTPCredential – the user is enabled for mobile app OTPs
• TransitionTextToAppHOTP – the user is enabled for both text message and mobile app OTPs

This result can be used to customize OTP prompt text (such as telling the user to expect an OTP via text message).

Transitioning

A user can be enabled for both text message and mobile app OTPs. This state is known as "transitioning". This is done so that a user can be enabled for two-factor authentication without having to install the mobile app immediately.

When a user is in the transitioning state, the pre-authenticate step will still send a text message OTP. A transitioning user can authenticate using either a text message or a mobile app OTP. When a transitioning user authenticates using a mobile app OTP for the first time, they will be automatically transitioned to only being enabled for mobile app OTPs (i.e. they will no longer be enabled for text message OTPs). This is done because mobile app OTPs are preferred to text message OTPs.

Advanced

Logging

The SDK uses Common.Logging for logging non-critical events. Common.Logging makes it easy to use your existing logging framework, see the Common.Logging website for more details: http://netcommon.sourceforge.net

Auditing

The SDK audits critical security events using an auditor that can be overridden. The default configuration writes audit events to logging.

The default logging auditor can be overridden as follows:

1. Create a new class that implements the IAuditor interface

1. Set the Auditor property of the TwoFactorConfiguration instance to an instance of your auditor class.