在Android应用程序中存储用户名和密码的最佳选择

I am developing an app where user needs to sign in to perform operations...but mostly on android handset ppl use "keep me signed in"...and in tht case I'll have to maintain the value of username and password within my app..should I use preferences, or SQLite Db or is there something else and how can I make it secure? Plz Help... Thanks in advance..I am developing an app where user needs to sign