Once the user has logged in using one of our SDKs as part of the response, you will get a JSON Web Token signed with the secret of that application.
For instance, in iOS:
[client loginAsync:self withCompletionHandler:^(BOOL authenticated) {
// client.auth0User.IdToken <--- this is the JWT
Or using Xamarin:
var user = await auth0.LoginAsync(this);
// user.IdToken <--- this is the JWT
Or in Windows Phone:
var user = await auth0.LoginAsync();
// user.IdToken <--- this is the JWT
For other examples, look under the Native Mobile App section.