How to integrate whole asp.net website with PHP?

Question

How to integrate whole asp.net website with PHP?

 

Actually i have two different websites  one is PHP and other is in Asp.net so what i want is when users are on PHP website and for some particular pages i need to use my asp.net website, when user click on button then user will redirect to asp.net website but the catch is i don't want to show url to user of my asp.net website, currently i am using iframe but i don't think so its and correct way to integrate there is some other reasons like security and all that with iframe? please suggest to do so? Thanx...