Each user who performs Dimensions configuration management operations via Stages needs a Dimensions user account. The user will be prompted once for his Dimensions credentials when they are needed. After successful authentication, Stages reuses the credentials for subsequent operations of the user, until an authentication attempt fails.
Beside the individual user accounts, one Dimensions account is needed by Stages for system and administrative operations. At the minimum this account needs read access to the items in all Dimensions projects/streams that are referenced in Stages.