code: func (m *MembershipsClient) List(ctx context.Context, orgID *identity.ID,
  	teamID *identity.ID, ownerID *identity.ID) ([]envelope.Membership, error) {
  
  	query := &url.Values{}
  	if orgID != nil {
  		query.Set("org_id", orgID.String())
  	}
  	if teamID != nil {
  		query.Set("team_id", teamID.String())
  	}
  	if ownerID != nil {
  		query.Set("owner_id", ownerID.String())
  	}
  
  	var memberships []envelope.Membership
  	err := m.client.RoundTrip(ctx, "GET", "/memberships", query, nil, &memberships)
  	return memberships, err
  }
docs: // List returns all memberships for a given organization, team, or user/machine