Hi JL,
In general, the users need not enter their password a second time when logging into Office 365.
I'd like to confirm the following things:
1. Which client do you use to access Office 365 account, Outlook or web browser?
2. Does this issue affect all users or only you?
Given this situation, please follow the steps below to troubleshoot this issue:
1. Install the latest Microsoft Online Services Sign-in Assistance.
2. If you access Office 365 by using web browser, please check "keep me signed in", and then test it again.
3. Test it in another web browser.
Thanks,
Edward Qu