Some help for those using Powershell to automate Azure Resource Manager but don't want to install the Azure Powershell Cmdlets or ADAL, enter credentials in a web browser popup or set up an application as a Service Principal....

Azure-AAD-Authentication-Rest.ps1

<#
.Synopsis
    Retrieves a token object from the Azure OAUTH2 service without launching a credentials window.
.DESCRIPTION
    Retrieves a token object that can later be used to authorise requests against the Microsoft Azure Resource Manager REST API.
.EXAMPLE
    Get-AzureOauth2Token -username 'aad.user@mydomain.onmicrosoft.com' -password 'P2ssw0rd'
#>
Function Get-AzureOauth2Token
{
  Param(
    [Parameter(Mandatory=$True)]
    [string]$username,
    [Parameter(Mandatory=$True)]
    [string]$password,
    [string]$servicePrincipal = "1950a258-227b-4e31-a9cf-717495945fc2"
    )

  $encodedUsername = [Security.SecurityElement]::Escape($username)
  $encodedPassword = [Security.SecurityElement]::Escape($password)

  $url = "https://login.windows.net/Common/oauth2/token"
  $data = @"
resource=https%3A%2F%2Fmanagement.core.windows.net%2F&client_id=$servicePrincipal&grant_type=password&username=$encodedUsername&password=$encodedPassword&scope=openid"
"@
  return Invoke-RestMethod -Uri $url -Method Post -Body $data
}

<#
.Synopsis
    Retrieves the accessible Azure subscriptions, given a valid access token.
.DESCRIPTION
    Lists the available Azure subscriptions via the Microsoft Azure Resource Manager REST API.
.EXAMPLE
    Get-AzureSubscriptions -accessToken 'access_token'
#>
Function Get-AzureSubscriptionRest
{
  Param(
    [Parameter(Mandatory=$True)]
    [string]$accessToken
    )

  $url = "https://management.azure.com/subscriptions?api-version=2015-01-01"
  $headers = @{Authorization=("Bearer {0}" -f $accessToken)}
  $rest = Invoke-RestMethod -Uri $url -Method Get -ContentType "application/json" -Headers $headers
  return $rest.value
}

# display valid Azure subscriptions 
$oauth2token = Get-AzureOauth2Token -username "aad.user@mydomain.onmicrosoft.com" -password "P2ssw0rd"
Get-AzureSubscriptionRest -accessToken $oauth2token.access_token | Format-Table subscriptionId, displayName, state