A client side form technology has to utilize some sort of access token based system where access token can be stored in cookie. A lot of modern OAuth2 based authentication systems like Windows Azure Active Directory, Salesforce, Google work on the same principle and is well supported by AgilePoint as it does support a concept of bring your own identity.
If it was a question of SSO only you could synchronize your OnPremises AD with windows Azure AD via ADFS and used it on AgilePoint portal whether it is hosted OnPrem or in cloud and that kind of solution is quite popular as this way you would have option of using Azure authentication in other solution as well. This is particularly good for clients who are in process of moving their OnPremises systems to cloud since Azure AD is supported by a lot of vendors.
However if your systems are mainly OnPremises, configuring Active Directory Federation Services (ADFS 3) is a good option as well. ADFS being a relatively complex configuration, I recommend working with AgilePoint services team to get it configured properly as they have helped numerous customers with ADFS 3.0 and ADFS 4.0 configuration.