using backslash (%5c) rest wcf url

i am building rest use wcf, methods i am minute getprofile, relapse form given username. username consolidate user's domain, have following format: "domain\username".

i therefore have use called profiles.svc, following endpoint set up:

[operationcontract]
[webget(uritemplate = "/{username}", responseformat = webmessageformat.xml)]
irestresponse getprofile(string username);

however, i try revisit use during (%5c urlencoded form backslash) i following error:

server blunder '/' application
http blunder 400 - bad request

this occurs even there formula indeed tangible doing getprofile, i trust blunder being thrown during indicate wcf attempts bond uri method.

are there settings i need supplement web use settlement method grant backslashes total urls rest wcf service? backslashes simply allowed?