Nauro, the Santander bank service, only accepts soap, does not work with https request, even using certificate. Using Linux, I tried with ruby (savon) and python (zeep), I only had success with nodejs, I got the client service authenticated using the certificate and passing the password. It does not serve certificate without an AC, certifying authority. I got the certificate from GlobalSign, type (PersonalSign 2 Pro), link , $ 89.00. After the completed purchase process, you will receive a pfx file, from which you can extract your certificate and your key, attaching them to your service.
Once you have the certificate in hand, you can access link and have the return of operations .
The choice of the PersonalSign 2 Pro plan is because it certifies the existence of the organization / company, this was requested by Santander.