Is there any non-manual way to change / bulk change user password?

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Customer is using Web Service SSO, so only IT know the users password and it is their security requirement that this know password for SSO need to be changed the periodically. If this cannot be done through some kind of automation (web service, import whatever means). Are you expecting them to change it by manually proxy the user login and change the password? Is there any non-manual way to change / bulk change user password? Please advice