RamKumar please keep in mind that angular and flarum don't actually authenticate anything; instead, they store a session / cookie variable that identifies you as a user to the server. You need to figure out how the backend you're using for your angular site authenticates, and then link that with Flarum. Theres a few options here, like setting up oauth/saml on your current site, or creating a custom extension on flarum to authenticate with your current site.
