We need your suggestions/inputs to implement the following use case:
Please let us know the approach to implement this. Also, let me know in case you need any other details.
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THe only option would be work with SAML and make all that tasks in a external system, and once authenticated redirect the user to appian via SSO..
I can only repeat my previous answer: "Not possible with OOTB Appian".
You will need some external infrastructure to make this working.