I've managed to find the answer looking at the code.
In case someone has the same need:
up.protocol.config.csrfHeader = "X-CSRFToken"; // Setting the variable will change the default CSRF header
up.protocol.csrfToken(); // Calling this will get the token from the meta tag as described on the docs
up.protocol.csrfParam(); // Calling this will get the param from the meta tag as described on the docs