code: func (c *Client) Login() (string, error) {
  	payload := &Request{
  		Action: "login",
  		Param: &LoginRequest{
  			CustomerNumber:  c.customerNumber,
  			APIKey:          c.apiKey,
  			APIPassword:     c.apiPassword,
  			ClientRequestID: "",
  		},
  	}
  
  	var responseData LoginResponse
  	err := c.doRequest(payload, &responseData)
  	if err != nil {
  		return "", fmt.Errorf("loging error: %v", err)
  	}
  
  	return responseData.APISessionID, nil
  }
docs: // Login performs the login as specified by the netcup WSDL
  // returns sessionID needed to perform remaining actions
  // https://ccp.netcup.net/run/webservice/servers/endpoint.php