I work on content management system, that has five antMatchers like the following:
http.authorizeRequests()
.antMatchers(\"/\", \"/*.html\")
I believe that the problem is in the order of your rules:
.antMatchers("/admin/**").hasRole("ADMIN")
.antMatchers("/admin/login").permitAll()
The order of the rules matters and the more specific rules should go first. Now everything that starts with /admin will require authenticated user with ADMIN role, even the /admin/login path (because /admin/login is already matched by the /admin/** rule and therefore the second rule is ignored).
The rule for the login page should therefore go before the /admin/** rule. E.G.
.antMatchers("/admin/login").permitAll()
.antMatchers("/admin/**").hasRole("ADMIN")