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Login-AzureRmAccount -SubscriptionId 'YOUR-GUID'
$uri = 'http://YOUR-URL'
$password = 'YOUR-PASS'

$app = New-AzureRmADApplication -DisplayName OctopusDeploySOMEAPPNAME -HomePage $uri -IdentifierUris $uri -Password $password
New-AzureRmADServicePrincipal -ApplicationId $app.ApplicationId
New-AzureRmRoleAssignment -RoleDefinitionName Contributor -ServicePrincipalName $app.ApplicationId