Attorney Gen says: (http://oag.ca.gov/firearms/pubfaqs#3
"As part of the DROS process, the buyer must present "clear evidence of identity and age" which is defined as a valid, non-expired California Driver's License or Identification Card issued by the Department of Motor Vehicles. A military identification accompanied by permanent duty station orders indicating a posting in California is also acceptable."
"Purchasers of handguns
are also required to provide proof of California residency, such as a utility bill, residential lease, property deed, or government-issued identification (other than a drivers license or other DMV-issued identification)."
Locks are required:
Penal Code 23635
"(a) Any firearm sold or transferred in this state by a
licensed firearms dealer, including a private transfer through a
dealer, and any firearm manufactured in this state, shall include or
be accompanied by a firearm safety device...."
Exceptions are available (own a safe; purchased lock within 30 days, etc)