Instructions :

$ brew install protobuf 
$ brew install go
$ go get -u github.com/golang/protobuf/{proto,protoc-gen-go}
$ go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-grpc-gateway
$ go get -u github.com/grpc-ecosystem/grpc-gateway/protoc-gen-swagger
$ go get -u -v google.golang.org/grpc
$ go get -u github.com/golang/protobuf/protoc-gen-go

Change the hardcoded GOPATH in build.sbt to sys.env("GOPATH")or hardcode it if you want to import the project in IntelliJ (haven't found a way for the embedded sbt to pick up on my .bashrc yet)

Make sure that $GOPATH/bin is in your path.

The reason that you have to install go is that the HTTP/REST gateway is written in go.

Run sbt compile. This will generate all the stubs (scala and go) from the proto definition that lives in src/main/protobuf/protocol.proto (Note that this naming is terrible), which defines the datatypes and the API methods.

Run sbt run and select the server to run the gRPC server written in Scala.

Run go run gateway/server/test.go to run the gateway server.

Run the following curl command to perform a request from the gateway

curl -X POST -H "Content-Type: application/json" -H "Cache-Control: no-cache" -H "Postman-Token: 1e813409-6aa6-8cd1-70be-51305f31667f" -d '{
     	"password" : "password"
     }' "http://127.0.0.1:8080/v1/johndoe64"

Run sbt run and select the client to run a native gRPC request against the gRPC server.