gcm map users, webview login

i map gcm reg id individual users on site.

what best way accomplish this?

i have webview in android loads site users required login, until login users anonymous can map users after login.

some thoughts are,

set user agent string reg id if not been registered, when logged in , if no id mapped user grab user agent string.

^^ seems easiest way me i'm beginner can think of flaws straight away.

monitor page url, if can done. when webview detects url "index.php"(user logged in) executes function within application send reg id server.

inject code hidden field in page before login , submit that?

i'm not sure if of these methods viable, appreciated. i'm still pretty beginner laymans terms appreciated.

you can pass data java code receives registration id (from google) web view using javascript, explained in answer this question.

or can load web view after getting registration id google. way can pass parameter url loading.

Detect