code: func (api *Client) SetGroupPurposeContext(ctx context.Context, group, purpose string) (string, error) {
  	values := url.Values{
  		"token":   {api.token},
  		"channel": {group},
  		"purpose": {purpose},
  	}
  
  	response, err := api.groupRequest(ctx, "groups.setPurpose", values)
  	if err != nil {
  		return "", err
  	}
  	return response.Purpose, nil
  }
docs: // SetGroupPurposeContext sets the group purpose with a custom context