Nobody has an answer?
Actually, I need to retrieve messages from the mail box, and I don't know how to do it if I can't access user data.
I saw that there is an API "Yahoo Mail Web Service" but I don't know if I can use it for Connected TV development (because I haven't found what I was looking for in JavaScript :(thank you for your help!

You cannot use the Yahoo! based login for this. They do not allow you for access to the ID's and Passwords entered into this area - it would be a huge security risk on their end. :DHope it help.