I'm is selling online trainings using WooCommerce store.
When the client buys the item, he's given an unique key, which he can use to start new training on a dedicated training website (another website, custom, Zend Framework based engine).
The training website has it own authentication mechanism and at this point user needs to register - create new account, providing email, new password etc.
At this point many users are confused, because they have just created new WooCommerce account to buy the key and now they don't know why the credentials don't work on this site too, why they need to create another new account.
The question is how can I simplify the user's life to have just one authentication process?
Eg. I have the credentials in the Wordpress (WooCommerce) database, and I use the same engine to login to my other website (trainings).
Are there any plugins to do this or docs on how to authenticate to external service using WooCommerce account?