The aries-framework-go project can be used as a DIDComm Router/Mediator. The agents that do not have inbound transport can register with the router. Basically, the agent asks another agent to route the messages to it by asking for permission. On successful grant, agent receives the endpoint and routing key details. These details are used in DID Exchange Invitation or DID Document Service Descriptor.
The project supports DIDComm between two agents without inbound capability through a router. The framework needs to be initialized with Transport Return route options.
// create the framework with Transport return route
framework := aries.New(aries.WithTransportReturnRoute(""all"))
Currently, framework supports limited set of features.