In SAP Service Cloud V2, the Source of a case (e.g., email, phone, social media) can be used as a condition to route a case to an employee. According to SAP documentation, "You can configure the rules to determine the Service Level for a certain ticket depending on several parameters like Ticket Type, Service Category, Source, Channel ID etc." Source is a standard attribute in routing rules to determine the appropriate employee or team.
Mashup (A) is used for external integrations, not routing. Autoflow (B) automates actions but does not route cases to employees. Input fields in the Case Designer (C) collect data but are not used for routing.
Reference:
SAP Community: Service Level Agreement in SAP Cloud for Customer community.sap.com SAP Help Portal: Case Routing Rules Configuration