Anybody still implementing PPTP deserves the insecurities that are inherent. A much more elegant, and secure, solution would just be tunneling via SSH dynamically. It's easy to do, requires no setup and if done right (i.e. certs for auth) it is a more maintainable solution. I generally use IPsec - because, it is still by and far, the most secure of the VPN solutions with platform interop today. Setting up and maintaining an IPsec tunnel for the masses is not trivial unfortunately - which is why I'd recommend SSH or potentially OpenVPN (which has nice IPv6 support).
The author of the article on how to implement references the below...
...I think there's plenty there to disuade you. Would you build your webapp on a framework that stores user credentials in plaintext as a feature? No. Enough said.
Why go through the trouble of implementing something that's known broken? sigh
