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Difficulty: MediumMicrosoft Identity Platform Authentication

You are developing a secure C# web application that runs on-premises. The application must sign in users and then call a downstream Web API on their behalf using the Microsoft Identity Platform.

The application is configured as a confidential client. You have already obtained the authorization code from the initial user login redirect.

You write the following code to initialize the application:

csharp
IConfidentialClientApplication app = ConfidentialClientApplicationBuilder.Create(clientId)
.WithClientSecret(clientSecret)
.WithRedirectUri(redirectUri)
.Build();

You need to complete the code to exchange the authorization code for an access token. Which code segment should you use?

  1. AuthenticationResult result = await app.AcquireTokenByAuthorizationCode(scopes, authorizationCode).ExecuteAsync();Answer
  2. B
    AuthenticationResult result = await app.AcquireTokenForClient(scopes).ExecuteAsync();
  3. C
    AuthenticationResult result = await app.AcquireTokenSilent(scopes, accounts.FirstOrDefault()).ExecuteAsync();
  4. D
    var credential = new DefaultAzureCredential(new DefaultAzureCredentialOptions { ManagedIdentityClientId = clientId });
    var tokenContext = new TokenRequestContext(scopes.ToArray());
    var token = await credential.GetTokenAsync(tokenContext);

Answer

AuthenticationResult result = await app.AcquireTokenByAuthorizationCode(scopes, authorizationCode).ExecuteAsync();
The application needs to exchange an authorization code for an access token to call a downstream API on behalf of a user. The app is a confidential client initialized as an IConfidentialClientApplication. The correct method to exchange the authorization code is AcquireTokenByAuthorizationCode, followed by ExecuteAsync to run the request.

Step-by-Step Solution

1
Identify the client type and the authentication flow needed.
The web application is a confidential client, and it must exchange an authorization code for a delegated user access token.
The scenario specifies a confidential client application that has already received an authorization code from a user login redirect.
2
Match the required flow to the correct MSAL.NET method.
Use the AcquireTokenByAuthorizationCode method of IConfidentialClientApplication.
This method is specifically designed to exchange the authorization code for access and refresh tokens.
3
Chain the MSAL builder execution method.
Append .ExecuteAsync() to the builder.
MSAL.NET uses a builder pattern, and .ExecuteAsync() must be called to send the asynchronous HTTP request to Microsoft Identity Platform.

Key Concept

Exchanging an authorization code for an access token using MSAL.NET ConfidentialClientApplication.
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Topics

Microsoft Identity Platform Authentication

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