send only password from stored credentials

I have found that, as an example, in trying to relog a user into Office 365 to activate local installations of office, the login is on 2 separate "pages."  On the first it requires the username, and on the second, it requires just the password.  So when I send credentials, it only sends the username (I assume it truncates full information, removing the password completely).  It would be great if there was an option to send only the password.  9 times out of 10, I know the username anyway...and just need the password.