If you are wanting to authenticate a friend to allow them to communicate/question your bot, I would suggest maintaining a credentials table. When the friend provides a unique credential you then enable additional commands for that session. This would all be unrelated to the LINE API.
I have a similar solution with my bot. Friends that are visible in special groups have additional bot commands available to them while general/unfamilar friends have a much smaller vocabulary of commands.
Send me a direct message if you have questions I haven't answered.
My way is login line after login your website and save line id(Line's userId) refer to your website account. When user chat in chat room , your webhook can get line id(Line's userId) and then you can verify/login with your line id(Line's userId) as your website account. If line id(Line's userId) is not in your table , you can just igore it.
hope you can understand my poor english :|