如何在运行时使用c＃设置凭据使用WS Security使用Web服务？

I'm developing a WCF project using C# and I need to consume a web service with ws-security. Problem is I will only know the credentials to use at run time immediatly before consuming the web service, so I can't really use the webconfig file to setup the soap header security section. I'm developing a WCF project using C# and I nee