从Web表单.aspx通过Azure活动目录登录

We got web form based application with database driven user login. Now we want to switch to windows Azure AD. I know i can create a new project and add authentication mechanism to use sign on using Azure AD (easy enough). But what i want is to modify my existing login mechanism to support Azure AD as well with old style login. So how can i do a simple aspx page code behind to login in Azure AD. I tried using ADAL library. I can popup login window via this (first line) We got web form based application with database