How to stop any existing user view a CPQ instance but still allow a tool to extract Quote info

Summary:

Recently one of customer's CPQ instance has been shutdown permanently. However, business has come back and said they'd still need a way to review quotes from that CPQ instance - they are fine with read only access. Even though we are creating a tool outside CPQ to extract quote information along with line details - we'd still like to ensure that CPQ instance can't be accessed by any user i.e., even if they try with previously saved url they shouldn't be able to access quotes from application and the newly created tool will be used only for that. Please suggest