Copy changes from quarkusio#1490 to the JWT guide

docs/src/main/asciidoc/security-jwt.adoc

@@ -359,21 +359,25 @@ import java.util.Arrays;
 import java.util.HashSet;
 
 import org.eclipse.microprofile.jwt.Claims;
-
 import io.smallrye.jwt.build.Jwt;
 
+/**
+ * A utility class to generate and print a JWT token string to stdout.
+ */
 public class GenerateToken {
+
     /**
-     * Generate JWT token
+     * Generates and prints a JWT token.
      */
     public static void main(String[] args) {
-        String token =
-           Jwt.issuer("https://example.com/issuer") // <1>
-             .upn("[email protected]") // <2>
-             .groups(new HashSet<>(Arrays.asList("User", "Admin"))) // <3>
-             .claim(Claims.birthdate.name(), "2001-07-13") // <4>
-           .sign();
+        String token = Jwt.issuer("https://example.com/issuer")
+                .upn("[email protected]")
+                .groups(new HashSet<>(Arrays.asList("User", "Admin")))
+                .claim(Claims.birthdate.name(), "2001-07-13")
+                .sign();
+
         System.out.println(token);
+        System.exit(0);
     }
 }
 ----