Design pattern for accessing static data

I have a scenario where I have a set of credentials for each environment e.g. for dev env username1/pwd1, for qa env username2/pwd2, for staging username3/pwd3 and so on. Now I want to create a class which will return me a set of credentials based on the env I feed to it. All the data has to go within code (as per my brilliant boss, no xml files and all), what design pattern I could use so that the code will be elegant and data can be made extensible in future?