Spring Boot HTTPSecurityConfiguration

I am trying to achieve the following:

1. Great access with any kind of login to a static /index.html
2. All other accesses need to be authorized

Base on my research so far I created the following HTTPSecurity configuration:

    http
        .csrf().disable()
        .authorizeRequests()
            .antMatchers(new String[]{"/", "/index.html"}).permitAll()
            .anyRequest().authenticated();

This, however seems only partly working since a call to localhost:8080/ is for some reason redirected to the blank page /auth. The call localhost:8080/index.html works.

What I am doing wrong here?

I am using Spring Boot 2.6.4.