Single Sign On between sites hosted in windows server and azure cloud

Hi,

I have 3 ASP.NET MVC websites sharing the same domain.

1. one.domain.com
2. two.domain.com
3. three.domain.com

These websites are exposed to customers. Customer need to log in to each website separately. I wish to provide common log in for all these sites using Single Sign On(SSO) so that if the customer is logged into one site, he/she will be automatically logged into other 2 sits also.

Website #1 and 2 are hosted in Microsoft Azure Virtual Machine with Windows Server OS(purchased VM) and website #3 is an Azure website (i.e hosted in Azure App cloud service). How to implement Single Sign On between websites 1/2 and 3?

Update:

I have implemented SSO between websites #1 and 2 as described below.

Web.config:

Used same cookie name ("SingleSignOn") and machine key values in web.config of both sites.

<authentication mode="Forms"><forms name="SingleSignOn" domain="domain.com" loginUrl="~/Account/Login" timeout="2880" /></authentication>
<machineKey decryption="AES" decryptionKey="xxxxxx....x" validation="SHA1" validationKey="xxxxx..x" />

Machine key is generated using IIS. But the environment is different for website hosted in Azure App(no IIS). Will SSO work in website #3, if above codes are used in web.config of website #3?

Thanks