Can I store id and password in a file and can I validate for every login

[tvnaidu]

I have this microcontroller based power readings project, I need to provide secure login id and password. I can keep id and password in a file, every login should check id and password with file, if it matches shopuld display my readings page itherwise not. basic login, incase if user wants to change password, there is serial console for COM port, can connect to COM port and edit that file for id and passoword. can I get some example HTML code?.

I don't have PHP/CGI/PERL support Here this web server povided GET and POST methods only. jave scripts are ok.

currently I did login page with hardcoded id and password, but I need to provide user changable password ( no chnage for id, but password should be user can chnage after login wth default id and password or edit the file directly for password through serial port using COM port)

[drhowarddrfine]

Neither html or css can do this.