Install Microsoft Online Services Sign-in Assistant

Install Windows Azure Active Directory Module for Windows PowerShell (64-bit version)

Windows Azure Powershell:
Connect-MSOLservice
(Enter administrator credentials)

Set password never expire for one user
Set-MsolUser -UserPrincipalName user@example.com -PasswordNeverExpires $true

Set password never expire for all users
Get-MSOLUser | set-msoluser -PasswordNeverExpires $true

Check all users PasswordNeverExpires status:
Get-MSOLUser | Select UserPrincipalName, PasswordNeverExpires

Source: Telstra Crowd Support

Technet