ASP.NET MVC with Azure B2C refresh ID token issue - asp.net-mvc

Question

I am developing an ASP.NET MVC app with Azure B2C authentication. It is required that, after the ID token expires (IIS session not expires), any subsequent action call should automatically refresh the ID token with the refresh token and then continue the execution without re-login.
Questions:
Does the solution make sense?
After refreshing the ID token and set the cookies, how can I redirect to the original url and continue execution without re-login?
Thanks, any idea is highly appreciated.
This is my code:
protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
{
var refreshToken = HttpContext.Current.Request.Cookies["msal.refreshtoken"];
if (refreshToken != null && !string.IsNullOrEmpty(refreshToken.Value))
{
var newIdToken = TokenService.RefreshIdToken(refreshToken.Value);
var idTokenCookie = new HttpCookie("msal.idtoken", newIdToken)
{
Secure = true,
HttpOnly = true
};
HttpContext.Current.Response.Cookies.Set(idTokenCookie);
return;
}
}
// TokenService.RefreshIdToken
public static string RefreshIdToken(string refreshToken)
{
var policyName = ConfigurationManager.AppSettings["ida:SignUpSignInPolicyId"];
var B2CDomain = ConfigurationManager.AppSettings["ida:B2CDomain"];
var tenant = ConfigurationManager.AppSettings["ida:Tenant"];
var clientId = ConfigurationManager.AppSettings["ida:ClientId"];
var clientSecret = ConfigurationManager.AppSettings["ida:ClientSecret"];
var tokenEndpointUri = $"https://{B2CDomain}/{tenant}/{policyName}/oauth2/v2.0/token";
var httpClient = new HttpClient();
var requestBodyDict = new Dictionary<string, string>
{
{ "grant_type" , "refresh_token" },
{ "client_id" , clientId },
{ "client_secret" , clientSecret },
{ "scope" , $"openid" },
{ "refresh_token" , refreshToken }
};
var request = new HttpRequestMessage
{
RequestUri = new Uri(tokenEndpointUri),
Method = HttpMethod.Post,
Content = new FormUrlEncodedContent(requestBodyDict)
};
var task = Task.Run(() => httpClient.SendAsync(request));
task.Wait();
var response = task.Result;
var task1 = Task.Run(() => response.Content.ReadAsStringAsync());
task1.Wait();
var responseString = task1.Result;
if (response.IsSuccessStatusCode)
{
var idToken = (string)JsonConvert.DeserializeObject<dynamic>(responseString).id_token.ToString();
return idToken;
}
else
{
throw new Exception();
}
}

Answer 1

A couple of thoughts that are too long to put in comments:
Yes the basic idea of ‘use the refresh token to get a new id token’ is how it’s supposed to work.
Googling this question suggests a bewildering array of examples to imitate :-( e.g. Microsoft’s Azure Samples on GitHub for A/D auth for a web app (as opposed to webapi or SPA)
The basic plan for identity problems like this is, find an authoritative example and follow it because that reduces your risk of embarrassing error. ( For instance, Auth0’s example for this scenario says to get a new refresh_token as well as a new id_token. Not doing that might be okay but then the user will be forced to re-login when the refresh token expires. Then you’ll be tempted to use ultra-long-lifetime refresh token, loosening your security a little)
If you can’t find an authoritative example, considering raising an issue or commenting on one.
OTOH, if the code you’ve written works, then maybe you’ve done!
The problem with finding an example to imitate after you’ve got started is trying to find just the right the example for the technology choices you already made. It may be easier to start with an empty project, follow a tutorial, get the tutorial working, then copy the solution back into your app.
To send your user back to their original target you should be able to
var originalUrl= HttpContext.Current.Request.Url;
HttpContext.Current.Response.Redirect(original);
But only do that if getting the id_token succeeded otherwise it creates an infinite loop.