I need to implement single authentication across multiple SS websites. These SS websites will be under the same URL, where each website is a sub-domain of the other.

Each of these websites will serve a specific purpose in terms of functionality so the subsites module doesn't provide what I need. I want to keep the databases for each website seperate.

Ideally I don't want to rely on external sources for authentication e.g. facebook or openid.

I am not sure what the best approach would be to implementing this. The desired design would be that users authenticate from one ss website which is like a gateway. Then from their they can navigate to the other websites without having to authenticate again at each website.

So if anyone has done something like this or has some ideas on how it could be implemented then please share.

I've just another look at the module and it looks like it supports silverstripe authentication as well. So you could set up one instance as the authenticator and point the others there. I've only used basic authentication though.