Authentication across sites

[tembalena]

I have 2 applications, and would like users to be authenticated in the one if logged in to the other. I've set both apps web.config settings for authentication and machinekey to be identical, and as far as I've read, that's all that's needed, however it's not working, I'm still being asked to login to the 2nd site when browsing to it from the 1st in which I'm logged in.

The web.config settings to be identical are as follows:
<authentication mode=&quot;Forms&quot;>
<forms name=&quot;.ASPXAUTH&quot;
protection=&quot;All&quot;
timeout=&quot;30&quot; />
</authentication>
<machineKey validationKey='...' decryptionKey='...' validation='SHA1'/>

(the machinekey validationKey and decryptionKey are values I generated using a site that generates these for you.)

Any help will be hugely appreciated.
Thanks!