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csharp products:
aspnet-core
ms-graph
azure-active-directory
name: This sample demonstrates using the Conditional Access auth context to perform step-up authentication for high-privilege and sensitive operations in a web app. urlFragment: ms-identity-dotnetcore-ca-auth-context-app description: "This sample demonstrates using the Conditional Access auth context to perform step-up authentication for high-privilege and sensitive operations in a web app."

Use the Conditional Access auth context to perform step-up authentication for high-privilege operations in a Web app

Overview
Scenario
Contents
Prerequisites
Setup
Registration
Running the sample
Explore the sample
About the code
Deployment
More information
Community Help and Support
Contributing

Overview

This code sample uses the Conditional Access Auth Context to demand a higher bar of authentication for certain high-privileged and sensitive operations in a Web App.

To use the CA Auth context in a Web API, please try the Use the Conditional Access auth context to perform step-up authentication for high-privilege operations in a Web API code sample

Scenario

The client ASP.NET Core Web App uses the Microsoft.Identity.Web and Microsoft Authentication Library for .NET (MSAL.NET) to sign-in a user with Azure AD.
For sensitive operations, the Web app can be configured to demand step-up authentication, like MFA, from the signed-in user

Overview

:information_source: Check out the recorded session on this topic: Use Conditional Access Auth Context in your app for step-up authentication

Prerequisites

Visual Studio
An Azure AD tenant. For more information see: How to get an Azure AD tenant
A user account in your Azure AD tenant. This sample will not work with a personal Microsoft account. Therefore, if you signed in to the Azure portal with a personal account and have never created a user account in your directory before, you need to do that now.
Azure AD premium P1 is required to work with Conditional Access policies.

Setup

Step 1: Clone or download this repository

From your shell or command line:

    git clone https://github.com/Azure-Samples/ms-identity-dotnetcore-ca-auth-context-app.git

or download and extract the repository .zip file.

:warning: To avoid path length limitations on Windows, we recommend cloning into a directory near the root of your drive.

There is one project in this sample. To register it, you can:

follow the steps below for manually register your apps
or use PowerShell

Step 2 (Setup with PowerShell script): Register the sample application(s) with your Azure Active Directory tenant:

automatically creates the Azure AD applications and related objects (passwords, permissions, dependencies) for you.
modify the projects' configuration files.

<details> <summary>Expand this section if you want to use this automation:</summary>

:warning: If you have never used Azure AD Powershell before, we recommend you go through the App Creation Scripts once to ensure that your environment is prepared correctly for this step.

On Windows, run PowerShell as Administrator and navigate to the root of the cloned directory
If you have never used Azure AD Powershell before, we recommend you go through the App Creation Scripts once to ensure that your environment is prepared correctly for this step.

In PowerShell run:

Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope Process -Force

Run the script to create your Azure AD application and configure the code of the sample application accordingly.
In PowerShell run:
```
cd .\AppCreationScripts\
.\Configure.ps1
```
Other ways of running the scripts are described in App Creation Scripts The scripts also provide a guide to automated application registration, configuration and removal which can help in your CI/CD scenarios.

</details>

Step 2 (Alternative Manual setup): Choose the Azure AD tenant where you want to create your applications

As a first step you'll need to:

Sign in to the Azure portal.
If your account is present in more than one Azure AD tenant, select your profile at the top right corner in the menu on top of the page, and then switch directory to change your portal session to the desired Azure AD tenant.

Register the client app (TodoListClient-authContext-webapp)

Navigate to the Azure portal and select the Azure AD service.
Select the App Registrations blade on the left, then select New registration.
In the Register an application page that appears, enter your application's registration information:
- In the Name section, enter a meaningful application name that will be displayed to users of the app, for example TodoListClient-authContext-webapp.
- Under Supported account types, select Accounts in this organizational directory only.
- In the Redirect URI (optional) section, select Web in the combo-box and enter the following redirect URI: https://localhost:44321/.
  
  Note that there are more than one redirect URIs used in this sample. You'll need to add them from the Authentication tab later after the app has been created successfully.
Select Register to create the application.
In the app's registration screen, find and note the Application (client) ID. You use this value in your app's configuration file(s) later in your code.
In the app's registration screen, select Authentication in the menu.
- If you don't have a platform added, select Add a platform and select the Web option.
- In the Redirect URIs section, enter the following redirect URIs.
  - https://localhost:44321/signin-oidc
- In the Front-channel logout URL section, set it to https://localhost:44321/signout-oidc.
Select Save to save your changes.
In the app's registration screen, select the Certificates & secrets blade in the left to open the page where we can generate secrets and upload certificates.
In the Client secrets section, select New client secret:
- Type a key description (for instance app secret),
- Select one of the available key durations (In 1 year, In 2 years, or Never Expires) as per your security posture.
- The generated key value will be displayed when you select the Add button. Copy the generated value for use in the steps later.
- You'll need this key later in your code's configuration files. This key value will not be displayed again, and is not retrievable by any other means, so make sure to note it from the Azure portal before navigating to any other screen or blade.
In the app's registration screen, select the API permissions blade in the left to open the page where we add access to the APIs that your application needs.
- Select the Add a permission button and then,
- Ensure that the Microsoft APIs tab is selected.
- In the Commonly used Microsoft APIs section, select Microsoft Graph
- In the Delegated permissions section, select the User.Read, Policy.Read.ConditionalAccess, Policy.ReadWrite.ConditionalAccess in the list. Use the search box if necessary.
- Note: The Graph permission, **Policy.ReadWrite.ConditionalAccess** is required for creating new auth context records by this sample. In production, the permission, **Policy.Read.ConditionalAccess** should be sufficient to read existing values and thus is recommended.
- Select the Add permissions button at the bottom.
- It is advisable to grant admin consent for these permissions here on this screen.

Configure the client app (TodoListClient-authContext-webapp) to use your app registration

Open the project in your IDE (like Visual Studio or Visual Studio Code) to configure the code.

In the steps below, "ClientID" is the same as "Application ID" or "AppId".

Open the TodoListClient\appsettings.json file.
Find the key Domain and replace the existing value with your Azure AD tenant name.
Find the key TenantId and replace the existing value with your Azure AD tenant ID.
Find the key ClientId and replace the existing value with the application ID (clientId) of TodoListClient-authContext-webapp app copied from the Azure portal.
Find the key ClientSecret and replace the existing value with the key you saved during the creation of TodoListClient-authContext-webapp copied from the Azure portal.

Running the sample

For Visual Studio Users

Clean the solution, rebuild the solution, and run it. You might want to go into the solution properties and set both projects as startup projects, with the service project starting first.

    cd TodoListClient
    dotnet run

Explore the sample

Configure the Auth context

We'd first replicate the experience of an admin configuring the auth contexts. For that, browse to https://localhost:44321 and sign-in using a tenant Admin account. Click on the Admin link on the menu.
As a first step, you will ensure that a set of Auth Context is already available in this tenant. Click the CreateOrFetch button to check if they exist. If they don't , the code will create three sample auth context entries for you. These three entires are named Require strong authentication, Require compliant devices and Require trusted locations.

Note: The Graph permission, Policy.ReadWrite.ConditionalAccess is required for creating new auth context records. In production, the permission, Policy.Read.ConditionalAccess should be sufficient to read existing values and is thus the only one recommended.

Select an operation in the Todo list controller and map it with an Authentication Context value. To apply click SaveOrUpdate. This updates this mapping in the local app's database.

Note: When changing auth context mappings, have the user sign-out and sign-back in for the changes to take effect.

Go to Current config link to get details of data saved on the Web API side in its database. You can Delete if you need to delete a mapping from the local database.

The web app is now ready to challenge users for step-up auth for the selected operations.

Configure a Conditional Access policy to use auth context in Azure portal

Navigate to Azure Active Directory> Security > Conditional Access
Select New policy and go to Cloud apps or actions. In dropdown select Authentication context. The newly created auth context values will be listed for you to be used in this CA policy.

Select the value and create the policy as required. For example, you might want the user to satisfy a MFA challenge if the auth context value is 'Medium'.

Test in the Web App

Browse https://localhost:44321 and sign-in.
Select TodoList page and perform the operations.

If an operation was saved for a certain authContext and there is a CA policy configured and enabled, the user will be redirected to Azure AD and ask to perform the required step(s) like MFA.

:information_source: Did the sample not work for you as expected? Then please reach out to us using the GitHub Issues page.

About the code

Code for the Web app (TodoListClient)

In Startup.cs, the following lines of code enables Microsoft identity platform endpoint to sign-in users.

services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
        .AddMicrosoftIdentityWebApp(Configuration, "AzureAd", subscribeToOpenIdConnectMiddlewareDiagnosticsEvents: true)

Additionally, the following lines of code this app to call MS Graph.


             .EnableTokenAcquisitionToCallDownstreamApi()
                 .AddMicrosoftGraph(Configuration.GetSection("GraphBeta"))
             .AddInMemoryTokenCaches();

In AdminController.cs, the method GetAuthenticationContextValues returns a default set of AuthN context values for the app to work with, either from Graph or a default hard coded set.

private async Task<Dictionary<string, string>> GetAuthenticationContextValues()
{
     Dictionary<string, string> dictACRValues = new Dictionary<string, string>()
        {
                {"C1","Require strong authentication" },
                {"C2","Require compliant devices" },
                {"C3","Require trusted locations" }
    };

    string sessionKey = "ACRS";

    if (HttpContext.Session.Get<Dictionary<string, string>>(sessionKey) != default)
    {
        dictACRValues = HttpContext.Session.Get<Dictionary<string, string>>(sessionKey);
    }
    else
    {
        var existingAuthContexts = await _authContextClassReferencesOperations.ListAuthenticationContextClassReferencesAsync();

        if (existingAuthContexts.Count() > 0)                 
        {
            dictACRValues.Clear();

            foreach (var authContext in existingAuthContexts)
            {
                dictACRValues.Add(authContext.Id, authContext.DisplayName);
            }

            HttpContext.Session.Set<Dictionary<string, string>>(sessionKey, dictACRValues);
        }
    }
    return dictACRValues;
}

CreateOrFetch method checks if auth context exists then retrieve the list from graph by calling ListAuthenticationContextClassReferencesAsync method else call CreateAuthContextViaGraph to create the auth context.

public async Task<List<Beta.AuthenticationContextClassReference>> CreateOrFetch()
{
    var lstPolicies = await _authContextClassReferencesOperations.ListAuthenticationContextClassReferencesAsync();

    if (lstPolicies?.Count > 0)
    {
        return lstPolicies;
    }
    else
    {
        await CreateAuthContextViaGraph();
    }
    return lstPolicies;
}

AuthenticationContextClassReferencesOperations.cs contains methods that call graph to perform various operations. In current sample we have used create and get methods. CreateAuthenticationContextClassReferenceAsync method creates the auth context: Note: this class calls the /beta endpoint of Graph as the API was available only on the /beta endpoint at the time of this sample's publishing

public async Task<Beta.AuthenticationContextClassReference> CreateAuthenticationContextClassReferenceAsync(string id, string displayName, string description, bool IsAvailable)
{
    Beta.AuthenticationContextClassReference newACRObject = null;

    try
    {
        newACRObject = await _graphServiceClient.Identity.ConditionalAccess.AuthenticationContextClassReferences.Request().AddAsync(new Beta.AuthenticationContextClassReference
        {
            Id = id,
            DisplayName = displayName,
            Description = description,
            IsAvailable = IsAvailable,
            ODataType = null
        });
    }
    catch (ServiceException e)
    {
        Console.WriteLine("We could not add a new ACR: " + e.Error.Message);
        return null;
    }

    return newACRObject;
}

ListAuthenticationContextClassReferencesAsync method get the existing auth context values from graph.

public async Task<List<Beta.AuthenticationContextClassReference>> ListAuthenticationContextClassReferencesAsync()
{
    List<Beta.AuthenticationContextClassReference> allAuthenticationContextClassReferences = new List<Beta.AuthenticationContextClassReference>();

    try
    {
        Beta.IConditionalAccessRootAuthenticationContextClassReferencesCollectionPage authenticationContextClassreferences = await _graphServiceClient.Identity.ConditionalAccess.AuthenticationContextClassReferences.Request().GetAsync();

        if (authenticationContextClassreferences != null)
        {
            allAuthenticationContextClassReferences = await ProcessIAuthenticationContextClassReferenceRootPoliciesCollectionPage(authenticationContextClassreferences);
        }
    }
    catch (ServiceException e)
    {
        Console.WriteLine($"We could not retrieve the existing ACRs: {e}");
        if (e.InnerException != null)
        {
            var exp = (MicrosoftIdentityWebChallengeUserException)e.InnerException;
            throw exp;
        }
        throw e;
    }

    return allAuthenticationContextClassReferences;
}

In TodoListController.cs, the method CheckForRequiredAuthContext retrieves the acrsvalues from database for the request method. Then checks if the access token has acrs claim with acrsValue. If does not exists then it creates a claims payload to be sent back to Azure AD.

        public string CheckForRequiredAuthContext(string method)
    {
        string claimsChallenge = string.Empty;

        string savedAuthContextId = _commonDBContext.AuthContext.FirstOrDefault(x => x.Operation == method && x.TenantId == _configuration["AzureAD:TenantId"])?.AuthContextId;

        if (!string.IsNullOrEmpty(savedAuthContextId))
        {
            HttpContext context = this.HttpContext;

            string authenticationContextClassReferencesClaim = "acrs";

            if (context == null || context.User == null || context.User.Claims == null || !context.User.Claims.Any())
            {
                throw new ArgumentNullException("No Usercontext is available to pick claims from");
            }

            Claim acrsClaim = context.User.FindAll(authenticationContextClassReferencesClaim).FirstOrDefault(x => x.Value == savedAuthContextId);

            if (acrsClaim?.Value != savedAuthContextId)
            {
                claimsChallenge = "{\"id_token\":{\"acrs\":{\"essential\":true,\"value\":\"" + savedAuthContextId + "\"}}}";
            
            }
        }

        return claimsChallenge;
    }

Code for the Web App (TodoListClient)

Methods in TodoListController.cs challenges the user to re-authenticate if a claims payload is returned by the CheckforRequiredAuthContext():

 string claimsChallenge = CheckForRequiredAuthContext("Delete");

if (!string.IsNullOrWhiteSpace(claimsChallenge))
{
    _consentHandler.ChallengeUser(new string[] { "user.read" }, claimsChallenge);
    return new EmptyResult();
}

Using Session State for better user experience

When the ChallengeUser() method is called, the redirect URL of the request sent to Azure AD will bring the user back to the /GET path. So the user might get confused if the authentication context was applied to an action like /CREATE. To make for a smoother user experience, we use the ASP.NET Session state to store the user's input. This allows us to restore the ToDo item once the user has come back to the web app after redirection.

Take a look into the example of using session state.

    // GET: TodoList/Create
    public ActionResult Create()
    {
        string claimsChallenge = CheckForRequiredAuthContext(Request.Method);
        if (!string.IsNullOrWhiteSpace(claimsChallenge))
        {
            _consentHandler.ChallengeUser(new string[] { "user.read" }, claimsChallenge);
            return new EmptyResult();
        }
        var todoObject = TodoSessionState(SessionAction.Get);
        if (todo != null && todoObject.IsInitialized())
        {
            PersistTodo(todoObject);
            TodoSessionState(SessionAction.Set);
            return RedirectToAction("Index");
        }
        Todo todo = new Todo() { Owner = HttpContext.User.Identity.Name };
        return View(todo);
    }
    // POST: TodoList/Create
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Create([Bind("Title,Owner")] Todo todo)
    {
        string claimsChallenge = CheckForRequiredAuthContext(Request.Method);
        if (!string.IsNullOrWhiteSpace(claimsChallenge))
        {
            _consentHandler.ChallengeUser(new string[] { "user.read" }, claimsChallenge);
            TodoSessionState(SessionAction.Set, todo);
            return new EmptyResult();
        }
        PersistTodo(new Todo() { Owner = HttpContext.User.Identity.Name, Title = todo.Title });
        return RedirectToAction("Index");
    }
    private Todo TodoSessionState(SessionAction action, Todo todo = null)
    {
        string todoObject = "Todo";
            switch (action)
            {
                case SessionAction.Set:
                    HttpContext.Session.SetString(todoObject, todo != null ? JsonSerializer.Serialize(todo) : "");
                    break;
                case SessionAction.Get:
                    var obj = HttpContext.Session.GetString(todoObject);
                    return !string.IsNullOrEmpty(obj) ? JsonSerializer.Deserialize<Todo>(obj) : null;
                default:
                    break;
            }
            return todo;
    }

More information

For more information about how OAuth 2.0 protocols work in this scenario and other scenarios, see Authentication Scenarios for Azure AD.

Community Help and Support

Use Stack Overflow to get support from the community. Ask your questions on Stack Overflow first and browse existing issues to see if someone has asked your question before. Make sure that your questions or comments are tagged with [azure-active-directory azure-ad-b2c ms-identity adal msal].

If you find a bug in the sample, raise the issue on GitHub Issues.

To provide feedback on or suggest features for Azure Active Directory, visit User Voice page.

Contributing

If you'd like to contribute to this sample, see CONTRIBUTING.MD.

This project has adopted the Microsoft Open Source Code of Conduct. For more information, see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.