@Nullable
    private BiPredicate<ClientRequestContext, String> allowedDomains() {
        if (allowedDomains != null) {
            final Set<String> allowedDomains0 = ImmutableSet.copyOf(allowedDomains);
            return (ctx, domain) -> {
                for (String d : allowedDomains0) {
                    // Use `equals()` to prevent Open Redirects.
                    // See https://www.acunetix.com/blog/web-security-zone/what-are-open-redirects/
                    if (domain.equals(d)) {
                        return true;
                    }
                }
                return false;
            };
        }
        return null;
    }
Returns a newly-created {@link RedirectConfig} based on the properties set so far.
core/src/main/java/com/linecorp/armeria/client/redirect/RedirectConfigBuilder.java