My idea was to add a button on the login page for marketing activities. The customer who registers should click the button to confirm that we are allowed to use the e-mail address for marketing activities. The setting should then be reflected in the CRM system so that we know who we can inform about news by e-mail.

In addition, the customer must also be able to change the setting in the account accordingly.

Is there a way to add such a button to the login page?

Or does anyone have another solution on how to implement the whole thing in the new system?