According to the university calls page:

https://personal.uca.es/convocatorias-de-capitulo-vi-2021/

“With respect to FOREIGN APPLICANTS WHO DO NOT HAVE A DIGITAL CERTIFICATE, the procedure to be followed will be as follows:

• The interested party must send an email to “seleccion.capitulovi@uca.es” indicating their interest in submitting an application to participate in the selective process for the recruitment of Research Staff and/or Research Support Technician and requesting their LDAP user keys. You must specify in the mail your NIF/NIE/Passport or identification document, your name, your first surname, your second surname (optional) and your e-mail address.
• Once the interested party is registered in the LDAP, he/she will be sent his/her user keys from the e-mail account “seleccion.capitulovi@uca.es”.
• Finally, the applicant will submit his/her application through the Virtual Office of the University of Cadiz
  https://oficinavirtual.uca.es/oficinaVirtual/EntradaOficinaVirtual?procedimiento=183
  using his/her LDAP user keys (these user keys can be used to track his/her file throughout the process until the end of the selection process, at which time he/she will be automatically removed from the LDAP).
• The application, in addition to all the documents listed in the Bases, shall be accompanied by “a scanned copy of the application signed by the interested party.”