How to Combine with custom's webservice api to achieved Single sign-on?

1.custom have own itself single sign-on system,can provide webservice api,such as: a. api url : http://10.50.11.100/MyWebSite/ProjectHome/WebService/DDLoginService.asmx?wsdl b.method: UserAuthenticateByDES() c.Request message: ************ d.Response message ： false as you know,splunk SSO only support saml & reverse proxy, so,my question is: how to Combine with custom's webservice api to achieved Single sign-on? any idea or reference?thanks a lot!!!