make abackup using CMD

Dears,

I need a help for the following case:

I want to make auto backup for the database using Dos Command line , I
made the following CMD line

pg-dumpall -h localhost -Upostgres > allinone.bak

but I found every time I have to enter password. So , how can I include
the password parameter in the above statement so that I can schedule
this patch to take a backup 4 times daily without entering the password
every time.

Thank you in advance for your support.

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