This can be accomplished by using Kerberos Delegation and setting the credentials for the datasource to Viewer Credentials before publishing.
This will require configuring Kerberos on both the Tableau Server and SSAS.
Please see these articles:
This video is useful for learning about Tableau's implementation of Kerberos:
Finally, if you do not have Kerberos available, you may want to look at:
Let me know if this helps or if you have any follow up questions!