Integrate websites, achieve single sign-on

[plengqui]

I would like to collect some best practices for the following challenge:

We have two separate websites with separate login and session management. They are on different platforms (eg one ASP and one PHP) and different databases. We have sourcecode for both.

We want to make the user feel as if it was one single website. The user should need to log in only once and then access his info on both websites freely, just as if he was surfing around on one single website.

What solutions do you know of to this problem?
What are the advantages and drawbacks of these solutions?

Here is one to start with:

Sync the user databases so that site A has access to login+pwd of site B. Let site A frame site B, and include the login+pwd of site B in the frame url, like this:
http://siteb/subdir/page.php?login=john&password=k3j4W3

[bathurst_guy]

Here is one to start with:

Sync the user databases so that site A has access to login+pwd of site B. Let site A frame site B, and include the login+pwd of site B in the frame url, like this:
http://siteb/subdir/page.php?login=john&password=k3j4W3
Very silly idea, not safe or secure at all.

Unfortunately I have no answer for your query though.

[plengqui]

Is it unsafe even if you use https on both sites?

A safer way may be for site A to send a session token to site B together with the user id and then have the frame url be something like this instead:
http://siteb/subdir/page.php?sessiontoken=oi33h4R8d3dXw

Comments?