Single sign-on with SocialEngine

We have an custom site built in PHP, with its own user account profiles/passwords/etc.

Potentially, we will be installing SocialEngine (based on PHP/Zend), but it is contingent on single sign-on capabilities.

Is there a plugin, or does SocialEngine otherwise accommodate allowing users who log into our "main" site to also get logged into SocialEngine? We are willing to modify the main site to the extent necessary.

There are a lot of questions around this, but no solid answers yet.

Can anyone provide some insight into how this could be done?

You can create your own class and integrate the Authenticate API like this:

class Api_Api_Auth extends Core_Api_Abstract {
public function userLogin($params) {
    // get user login parameter

    // your implementation

    // check the user have existing account and user is verified clause
    // your implementation
    $authResult = $this->authenticate ( $username, $password );
    $authCode = $authResult->getCode ();
    // user login status
    $success = Zend_Auth_Result::SUCCESS;

    // login success user date
    // your implementation

    // return user data
    // your implementation
    return $loggedin;
}

}