@Override
    public String toString() {
        if (toString == null) {
            toString = rawResponse();
        }
        return toString;
    }
{@code JSON}-formatted raw Token Introspection Response body. If the {@link OAuth2TokenDescriptor} was
not parsed out of the raw response body, this value calculated based on the other
{@link OAuth2TokenDescriptor} values.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/OAuth2TokenDescriptor.java