#Connect to Exchange Online
$userCredential = Get-Credential
$Session = New-PSSession -ConfigurationName Microsoft.Exchange -ConnectionUri https://ps.outlook.com/powershell/ -Credential $usercredential -Authentication Basic –AllowRedirection
Import-PSSession $Session
#View User's Calendar permissions
Get-MailboxFolderPermission username:\calendar
#Add permissions for a user
Add-MailboxFolderPermission -Identity user1@domain.com:\calendar -user user2@domain.com -AccessRights Editor
#Verify Permissions
Get-MailboxFolderPermission username:\calendar
#Exit/Disconnect Session
Remove-PSSession $Session