You are a solution architect and your client has recently completed a merger and acquisition. Your client uses SAP S/4HANA Cloud Public Edition and the acquired company is using SAP ECC 6.0. For business and legal reasons, the users of the acquired company cannot yet be added to the global user directory. The acquired users still need access to the custom application.
Given the attached diagram, which solution would you recommend to your client in "1" to enable this access?