A Web Application's Login Form and Signup Form blocks can offer "Continue with Google", "Continue with GitHub", "Continue with Apple", "Continue with Microsoft", and "Continue with Facebook" buttons alongside the normal email/password fields, letting your app's own visitors sign in without choosing a new password.
What you need to connect first
Each provider is your OWN connection, registered from your Integrations settings, not something CodeBlock Studio shares across every project. For Google, GitHub, Microsoft, and Facebook, you paste a client ID and client secret from that provider's own developer console. For Apple, you paste four separate values instead, a Services ID, a Team ID, a Key ID, and a private key, since Apple doesn't use a single static secret. A button for a provider you haven't connected yet simply doesn't appear on your Login Form or Signup Form, nothing breaks, there's just one fewer option shown.
A real limitation worth knowing
Because the redirect URL each provider needs is one fixed address, a completed sign in always lands the visitor back on your app's default CodeBlock Studio address, even if you've connected a custom domain (see "Connecting a custom domain"). Email/password sign in isn't affected, only the social sign in redirect step.
Tip: If a visitor signs up with any of these providers using the same email as an existing password account, it becomes the same account, see "Signing in with Google vs. email and password" for the equivalent behavior on your own CodeBlock Studio account.