Not “pure server” no. You need to authenticate whenever your token+refresh is completely dead.
A Twitch user access token is valid for 4 hours.
When that token dies you can use a refresh token to generate a new token.
A refersh token has no expiraration at time of writing (and when you refresh you may get a new refresh token).
So you only need to do the webpage when you have no token/all tokens are dead.
From then on it’s all server.
Unless something causes the refresh token to be invalid, then you’ll have to webpage again to get new keys