There are a couple of high level approaches:
Security:
- Put a web server in front of both Plone and the ASP.net application and use the auth_tkt cookie format. Apache and nginx support this, for example, and Plone 4 has built-in auth_tkt cookie format support.
- Use a shared ActiveDirectory/LDAP repository to share account id, roles, etc.
Content:
- Use something like ore.contentmirror to export content from Plone to a database and render through the ASP.NET application
- Use a Plone view to render only what you want and either scrape this into the ASP.NET application or use an
<iframe />
to render it.
- Use Diazo (XDV) at the web server level to merge the two applications visually - this will work best if entire areas of the site are to be served by Plone rather than just pulling in some content here and there.