Combine 302 and canonical link, according to Google's Maile Ohye

[suzukik]

Maile Ohye from Google tweeted as follows [twitter.com]:

302s (not 301s) are fine as canonicals. So example.com/ can 302 to example.com/session.php which rel=canonical's to homepage.

JohnMu once told about 302 redirect for domain root [webmasterworld.com]. The combination explained by her made his method one step further.

[tedster]

Makes plenty of sense - especially if the tracking technology is adding session IDs to the URL. That situation has tripped up many a website's indexing. This way Google knows the canonical and the user still gets their session.