ADFS 2016 On behalf of flow : cannot get any user informations - .net-core

Question

I'm trying to implement the "on behalf of" flow in an application using ADFS 2016 as STS. As a reference, I look at this Microsoft tutorial (https://learn.microsoft.com/en-ca/windows-server/identity/ad-fs/development/ad-fs-on-behalf-of-authentication-in-windows-server). It's working as it should, I can login into my web application and then use my original access token in UserAssertion to generate a new access token with the proper audience to call my API BUT I found absolutely no way to include any user informations (sub, name, email, upn etc.) into the access token for my API, even if I set claim rules into my ADFS configurations for the API.
I checked the communication between my app and adfs using Fiddler and everything looks like the informations in the tutorial. See the screen shot of the "on behalf of" request below :
Here's the resulting access token :
Finally, here's the code I use to generate my new access token :
private async Task<string> GetAccessToken(ClaimsPrincipal user, string originalAccessToken)
{
var authority = "[authority]";
var context = new AuthenticationContext(authority, false);
string userName = user.FindFirstValue("upn");
var userAssertion = new UserAssertion(originalAccessToken, "urn:ietf:params:oauth:grant-type:jwt-bearer",userName);
var cc = new ClientCredential("https://localhost:44387/", "[client_secret]");
var result = await context.AcquireTokenAsync("https://localhost:44339/", cc, userAssertion);
return result.AccessToken;
}
Have you struggle with that scenario and if yes, did you find a way to fix this ?
Thanks

Answer 1

I've only used the Microsoft On Behalf Of flow with Azure AD and not ADFS, but it looks like you need to send a more detailed scope in your User Info request.
Maybe try sending 'openid profile email', to indicate that you want that type of detail, as in Section 17 of my blog post. Of course this assumes that this type of data has been registered for all users.
TROUBLESHOOTING
Looks like one of these will be the cause:
A suboptimal Microsoft library that does not allow you to send the required scope
Or ADFS 2016 perhaps lacks the scope features that work correctly in Azure AD
I would concentrate on making extra sure you are sending the correct form URL encoded request message, using a tool such as curl, Postman or a plain C# HttpClient. Here is the code I used to send the correct scope - using an open source library rather than a Microsoft one:
Sample NodeJS Code
If you can get the scope sent correctly then you should have a resolution either way:
Either you get the correct data and can update your code
Or the behaviour you want is not supported by ADFS
Good luck ...