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Implementing an OAuth client credentials flow with ADFS–Part 3–Debugging the flow

It looked like most of the world has made the switch to Microsoft Entra(Azure Active Directory). However one of my clients is still using ADFS. Unfortunately there isn't much information left on how to get an OAuth flow up and running in ADFS. Most of the links I found point to documentation that no longer exists. So therefore this short blog series to show you end-to-end how to get an OAuth Client Credentials flow configured in ADFS.

Part 1 - ADFS configuration

Part 2 – Application configuration

Part 3 (this post) – Debugging the flow

In the first 2 posts I showed you the happy path. So if you did everything exactly as I showed, you should end up with a working Client Credentials flow in ADFS. Unfortunately there are a lot of small details that matter, and if you make one mistake you’ll end with a wide range of possible errors.

In today’s post, I focus on the preparation work to help us debug the process and better understand what is going on.

Updating your OAuth Configuration to improve the debugging experience

The trick to understand what is going is to register to the different events that are triggered by the authentication middleware. ASP.NET Core uses a standardized approach so what I’m showing here can also be applied to other types of authentication(although the specific events and parameters can differ).

In our case we need to provide a JwtBearerEvents instance where we can subscribe to the following events:

  • OnAuthenticationFailed : Invoked if authentication fails during request processing. The exceptions will be re-thrown after this event unless suppressed.
  • OnChallenge : Invoked before a challenge is sent back to the caller.
  • OnForbidden : Invoked if Authorization fails and results in a Forbidden response.
  • OnMessageReceived : Invoked when a protocol message is first received.
  • OnTokenValidated : Invoked after the security token has passed validation and a ClaimsIdentity has been generated.

Here is an example implementation where I output the parameters to the console:

We’ll use this class in our next post to capture any error and better understand what is going wrong.

More information

IJwtBearerEvents Interface (Microsoft.AspNetCore.Authentication.JwtBearer) | Microsoft Learn

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