Background

Having contained databases was a step towards providing software as a service (SaaS). By having a contained database and contained users, multiple database instances of Synergetic can be installed on the same SQL instance, each of which contains data of which will not be accessible by users of other databases.

This was a change from previous instances of Synergetic where users and roles resided on the server level.

Server level logins

Rather than have a login at the contained database level, an alternative approach could be to remove any accounts from the contained (single) database, as well as the synonym databases, and then give permission at the server level account access the contained database/s as required. This eliminates the possibility of passwords becoming out of synch.

This might be an approach taken where you have a bespoke integration querying from the Synergetic single database and other databases that reside on the database server.

Source/s:

https://docs.microsoft.com/en-us/sql/relational-databases/databases/contained-databases