ADFS Authentication Fails only when using Fiddler

2 posts, 0 answers
  1. Patrick
    Patrick avatar
    1 posts
    Member since:
    Apr 2019

    Posted 16 Apr 2019 Link to this post

    I have a single ADFS server that is part of an Active Directory domain.  I'm having an issue with a Federated application and have turned to Fiddler to troubleshoot (as I have done in the past) and all of a sudden I'm seeing a strange issue that wasn't happening before.

    I'm using fiddler on an administration desktop, so I log on with an admin account, this means when I try to use SSO for a federated app, when I hit ADFS it prompt for authentication.  Normally, great no problem, I put in my normal username / password (not the admin account I'm logged on with) it authenticates and off I go to the federated app.  This has been working fine for sometime but then recently its started to fail. It never accepts my username / password, just keeps 401, 401, 401, prompting me for username / password again and again.

    I know my username / password are fine as I use them every day to log onto my desktop AND it only fails when I have fiddler open. If I close fiddler, I get prompted, enter my creds and it works fine.

    It also doesn't matter what browser I use.

    Does anyone know what this is? Or know how I can troubleshoot it / gather more info?






  2. Simeon
    Simeon avatar
    241 posts

    Posted 19 Apr 2019 Link to this post

    Hi Patrick,

    You have to track down what have changed in the whole picture when the ADFS authentication started to fail. It could be an update/modification of the ADFS server, the SSO process, the federated app, Fiddler, FiddlerScript, AutoResponse rule, expired cookie, a client certificate renewal etc.

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