I’m writing a mostly ajax-driven web application and I’m looking at how to protect the user from CSRF attacks. I’m planning to run the pages of the application where the user is logged in to do his work in HTTPS mode.
Does running the page on HTTPS work to protect against CSRF attacks?
No, running a page on HTTPS does not protect it from CSRF. The fact that the communications between the browser and server is encrypted has no bearing on CSRF.
I suggest reading the OWASP guidance on preventing CSRF.