code: func New(ctx Context, cfg fab.ChannelCfg) (fab.ChannelMembership, error) {
  	mspManager, mspNames, err := createMSPManager(ctx, cfg)
  	if err != nil {
  		return nil, err
  	}
  	return &identityImpl{mspManager: mspManager, msps: mspNames}, nil
  }
docs: // New member identity