public final HttpAsyncClientBuilder setUserTokenHandler(final UserTokenHandler userTokenHandler) {
        this.userTokenHandler = userTokenHandler;
        return this;
    }
Sets {@link UserTokenHandler} instance.
<p>
Please note this value can be overridden by the {@link #disableConnectionState()}
method.
</p>

@return this instance.
httpclient5/src/main/java/org/apache/hc/client5/http/impl/async/HttpAsyncClientBuilder.java