Postman and CAS authentication - Has anyone been able to access a "backdoor" to do a direct login...

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Our Production and Test instances have CAS enabled on them. Any manually created accounts use a backdoor to log into the LE (instance.desire2learn.com/d2l/login?noRedirect=1) I am trying to request an OAuth 2.0 token for my API collection in Postman as outlined in this article but the token login page keeps directing to the CAS login not the 'backdoor'. Any thoughts?