Support double opt in

First: Thank You for the module!

Due to double opt in (which is mandatory in the EU) it would be great, that the module supports the creation of a customized confirmation link and also sending it via the mailjet API (the module should then depend on the mailjet module which supports this: https://www.drupal.org/project/mailjet →

also the module should collect explicit consent from the subscribers to comply with the GDPR
= a checkbox the users must check it to subscribe (value should be saved in mailjet.

here would be a toturial, what has to be done, that den EU Double Opt-In System could work with mailjet and your module.
https://www.mailjet.com/blog/news/how-to-set-up-a-double-opt-via-mailjet...

thx!