如何安全地在应用程序中保存密码?

I made a site where people can sign in and 'do something'. Now I want to create Android application which be a client apk (people could do things similar to page).

Question:

  1. Php is server-side language, so its more secure to store passwords (for ex. to mysql) in .php than in android apk. Which are the best way to store passwords in android application?