We are thinking to move some of our intranet sites to public cloud.
Is there any way to keep using company SSO to authorize access to those sites from the company intranet?
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Sure it's possible. What you want to do is called Federation. How you set it up really depends on the applications and platforms you run though. There are a variety of protocols out there that can do what you want; e.g. SAML, WS-Federation, OpenAuth (to a degree), etc.
The applications need to be able to support the federation protocols though.
In theory you could also set up a VPN from the cloud provider to your intranet too.
If you are running an Active Directory domain you can use Active Directory Federation Services (v2) from Microsoft (http://msdn.microsoft.com/en-us/security/aa570351), and that will let you federate using SAML or WS-Fed to applications that support the protocol. If you are running another directory service there are a few other providers out there like PingFederate (https://www.pingidentity.com/). You could also use a product like (Full disclosure: I work for the company) AuthAnvil SSO (http://www.scorpionsoft.com/).
The questions you need to ask: