Token Exchange Types

Summary

Token exchange is the process of exchanging one type of security token for another. It is a crucial aspect of authorization in modern web-based applications and services. There are several types of token exchange protocols, including OAuth, SAML, JWT, and Kerberos.

In our example, we’ll look at how to perform a token exchange using C# and the OAuth 2.0 protocol. We’ll use the HttpClient class to send a request to the Azure AD token endpoint and pass in the client ID, client secret, grant type, assertion (access token), and target resource as parameters in the request body. Once we received the response from the token endpoint, we parsed the JSON content and extracted the access token.

It’s worth noting that token exchange is an important part of securing web-based applications and services, but it’s just one piece of the puzzle. Developers need to carefully consider the security implications of their token exchange implementation, as well as the overall architecture of their application or service. By following best practices and using established security protocols, developers can build robust and secure applications that protect users and their data.

Token Exchange Types

1. OAuth token exchange: OAuth is a popular protocol used for authorization and token exchange in web-based applications. With OAuth, a user can grant permission to an application to access their resources on a service provider, and the application receives an access token in exchange. The access token can be exchanged for another token, such as a refresh token, or a different type of access token with different scopes or permissions.
2. SAML token exchange: Security Assertion Markup Language (SAML) is a protocol used for exchanging security tokens between parties. With SAML, a user can authenticate to a service provider using a SAML token, and the service provider can exchange that token for another token, such as a SAML assertion or a different type of security token.
3. JWT token exchange: JSON Web Tokens (JWT) are a popular format for representing claims securely between parties. With JWT, a user can authenticate to a service provider using a JWT token, and the service provider can exchange that token for another token, such as an OAuth access token or a SAML assertion.
4. Kerberos token exchange: Kerberos is a protocol used for authentication between computers in a network. With Kerberos, a user can authenticate to a service using a Kerberos ticket, and the service can exchange that ticket for another ticket, such as a Service Ticket or a Ticket-Granting Ticket, to access different resources.
5. Custom token exchange: Some applications or services may use their own custom security tokens, which can be exchanged for other tokens using a custom token exchange process.

Example

Here’s an example of how to perform a token exchange using C# and the OAuth 2.0 protocol:

using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading.Tasks;

public async Task<string> ExchangeToken(string accessToken, string targetResource)
{
    string tokenEndpoint = "https://login.microsoftonline.com/{tenant-id}/oauth2/token"; // replace {tenant-id} with your Azure AD tenant ID
    string clientId = "your-client-id"; // replace with your Azure AD app client ID
    string clientSecret = "your-client-secret"; // replace with your Azure AD app client secret

    HttpClient client = new HttpClient();

    // set the request parameters
    var content = new FormUrlEncodedContent(new[]
    {
        new KeyValuePair<string, string>("client_id", clientId),
        new KeyValuePair<string, string>("client_secret", clientSecret),
        new KeyValuePair<string, string>("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer"),
        new KeyValuePair<string, string>("assertion", accessToken),
        new KeyValuePair<string, string>("resource", targetResource)
    });

    // send the request to the token endpoint
    HttpResponseMessage response = await client.PostAsync(tokenEndpoint, content);

    // read the response and extract the access token
    string responseContent = await response.Content.ReadAsStringAsync();
    var token = JObject.Parse(responseContent)["access_token"].ToString();

    return token;
}

In this example, we use the HttpClient class to send a request to the Azure AD token endpoint. We pass in the client ID, client secret, grant type, assertion (access token), and target resource as parameters in the request body.

Once we receive the response from the token endpoint, we parse the JSON content and extract the access token. Finally, we return the access token as a string.

Note that this example assumes that you have already obtained an access token using some other means, such as using the Azure AD authentication libraries. The accessToken parameter should contain the access token that you want to exchange for a different type of token. The targetResource parameter should contain the URI of the resource that the new token will be used to access.