May be it is an OOP solution

HowToFightSpringSecurity.java

class Account {
    private String email;
    private String password;

    // single method
    public UserDetails asDetails() {
        return new AccountDetails() {
            @Override public String getPassword() {
                return Account.this.password;
            }
            @Override public String getUsername() {
                return Account.this.email;
            }
        };
    }
}

abstract class AccountDetails implements UserDetails {
    public final Account account;

    public AccountDetails(Account account) { this.account = account; }

    // template code vvv
    @Override public Collection<? extends GrantedAuthority> getAuthorities() { return null; }

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

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

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

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