Cannot Initiate SP-initiated Flow through Excel

Document ID : KB000130862
Last Modified Date : 12/04/2019
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Issue:
Unauthenticated users are submitting an SP-initiated federation request via Excel.  The SSO/Siteminder login page is presented as expected, but upon submitting credentials, the form seems to hang forever, never closing or updating.
Cause:
Siteminder html forms authentication requires a full http client.  Although Excel is able to perform some http client tasks, it is unable to authenticate via SSO/Siteminder's html forms authentication. Tasks that the client is required to perform include following 302 redirects, posting data to forms, and accepting transient and persistent cookies.
Resolution:
This is not a supported use case as html forms authentication requires a full http client.