func (b *BackendPlugin) Server(broker *plugin.MuxBroker) (interface{}, error) {
	return &backendPluginServer{
		factory: b.Factory,
		broker:  broker,
		logger: b.Logger,
	}, nil
}
Server gets called when on plugin.Serve()
package plugin
import (
	"context"
	"net/rpc"
	"sync/atomic"
	"google.golang.org/grpc"
	log "github.com/hashicorp/go-hclog"
	"github.com/hashicorp/go-plugin"
	"github.com/hashicorp/vault/logical"
	"github.com/hashicorp/vault/logical/plugin/pb"
)
type BackendPlugin struct {
	Factory      logical.Factory
	metadataMode bool
	Logger       log.Logger
}