Any suggestions on electronic means to prove my identity?

It is recommended to have an electronic certificate. You can get it for free at the Torrevieja Town Hall. To do this, you will need an appointment that you can request in person at the registry/PROP (Plaza Constitución 5, Torrevieja, better to go early, before 09:00 a.m.) or electronically, in the latter case you do not need to prove your identity through means electronics.

The Cl@ve system is also a good option, also available through Registration/PROP.