Are you legally allowed to refuse to give them a CPL? Of course. You are not concealing so there is no need to show them. As far as your ID? It all depends on how comfortable you feel about it. Like it or not, someone openly carrying a firearm is not something a lot of people are usedto seeing.
If for some reason you are asked by a cop and are detain, politely point out that open carry is legal in Washington state andthat you are not doing anything illegal and ask if you are being detained. If they say no, then tell them you are leaving and tohave a good day. If they say yes, I personally would comply with all requests andthen file a complaint with the department.
Remember, openly carryinga firearm may be a new and exciting for you. It will take you a bit to feel completely comfortable in public andnot fearing of a visit from Johnny Law. No pun intended, Johnny Law.
Welcome to the forums, and remember you represent us as a whole as well.