Save user information

API
15

With javascript on the page

        if (document.location.hash && document.location.hash != '') {
            var parsedHash = new URLSearchParams(window.location.hash.substr(1));
            if (parsedHash.get('access_token')) {
                var access_token = parsedHash.get('access_token');
                document.getElementById('access_token').textContent = 'Your Access Key from the #url: ' + access_token;

From the example I linked to https://github.com/BarryCarlyon/twitch_misc/blob/main/authentication/implicit_auth/index.html#L31-L35

Once you have it in a JS var you can do what you want with it