Cannot login with Spring Boot Security

I have a Spring Boot app with MySQL. I can save Users in the database but when I try to login, it keeps saying that the username or password is incorrect. Even when I hard code an User, it still doesn't work.

I created the setup using the JavaBrains tutorial and their code on GitHub.

This is the code I'm using.

Security config:

@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    @Autowired
    UserDetailsService userDetailsService;

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.userDetailsService(userDetailsService);
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http
                .authorizeRequests(authorize -> authorize
                        .antMatchers("/static/**", "/index").permitAll()
                        .antMatchers("/premium/**").hasAuthority("PREMIUM")
                        .antMatchers("/user/**").hasAuthority("USER")
                )
                .formLogin(formLogin -> formLogin
                        .loginPage("/login")
                        .failureUrl("/login-error")
                );
    }

    @Bean
    public PasswordEncoder getPasswordEncoder() {
        return NoOpPasswordEncoder.getInstance();
    }
}

My UserDetailsService

public class MyUserDetailsService implements UserDetailsService {

    @Autowired
    UserRepository userRepository;

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        Optional<User> user = userRepository.findByUsername(username);
        user.orElseThrow(() -> new UsernameNotFoundException("Can't find user " + username));
        return user.map(MyUserDetails::new).get();
    }
}

My UserDetails

public class MyUserDetails implements UserDetails {

    private String username;
    private String password;
    private boolean isEnabled;
    private List<GrantedAuthority> authorities;

    public MyUserDetails(User user) {
        this.username = user.getUsername();
        this.password = user.getPassword();
        this.isEnabled = user.isEnabled();
        this.authorities = Arrays.stream(user.getAuthorities().split(","))
                .map(SimpleGrantedAuthority::new).collect(Collectors.toList());
    }

    @Override
    public Collection<? extends GrantedAuthority> getAuthorities() {
        return authorities;
    }

    @Override
    public String getPassword() {
        return password;
    }

    @Override
    public String getUsername() {
        return username;
    }

    @Override
    public boolean isAccountNonExpired() {
        return true;
    }

    @Override
    public boolean isAccountNonLocked() {
        return true;
    }

    @Override
    public boolean isCredentialsNonExpired() {
        return true;
    }

    @Override
    public boolean isEnabled() {
        return isEnabled;
    }
}

My UserRepository

@Repository
public interface UserRepository extends JpaRepository<User, Long> {

    Optional<User> findByUsername(String username);

}

User

@Entity(name="Users")
public class User {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;
    private String username;
    private String password;

    @Transient
    private String passwordConfirm;
    private boolean isEnabled;
    private String authorities;
    private String isPremium;
    private LocalDateTime premiumExpiryDate;

    // getters and setters
}

Login form on the login page

<p th:if="${loginError}" class="error">Wrong user or password</p>
<form th:action="@{/login}" method="post" class="login100-form validate-form p-l-55 p-r-55 p-t-178">
        <span class="login100-form-title">
            Sign In
        </span>

    <div class="wrap-input100 validate-input m-b-16" data-validate="Please enter username">
        <input class="input100" type="text" name="username" placeholder="Username">
        <span class="focus-input100"></span>
    </div>

    <div class="wrap-input100 validate-input" data-validate = "Please enter password">
        <input class="input100" type="password" name="password" placeholder="Password">
        <span class="focus-input100"></span>
    </div>

    <div class="text-right p-t-13 p-b-23">
            <span class="txt1">
                Forgot
            </span>

        <a href="#" class="txt2">
            Username / Password?
        </a>
    </div>

    <div class="container-login100-form-btn">
        <button class="login100-form-btn">
            Sign in
        </button>
    </div>
</form>

I don't have a POST mapping for the login as it is supposed to be provided by Spring security. However I suspect the problem must be somewhere there, because I had log statements in the UserDetails and in the UserDetailsService but none of those got invoked.

Can you help me figure out what is the problem here?