Get-AADToken.ps1

# Original code from https://github.com/slavizh/OMSSearch/blob/master/OMSSearch.psm1
# - Updated/fixed authentication method calls
# - Ensure ADAL DLL is loaded

Function Get-AADToken {
<#
    .SYNOPSIS
        Get token from Azure AD so you can use the other cmdlets.
    .DESCRIPTION
        Get token from Azure AD so you can use the other cmdlets.

    .PARAMETER OMSConnection
        Object that contains all needed parameters for working
        with OMSSearch Module. You can create such object in
        OMS Automation as connection asset.
    .PARAMETER TenantADName
        Valid Azure AD Tenant name.
        Example: stanoutlook.onmicrosoft.com
    .PARAMETER TenantID
        Valid Azure Tenant ID.
        Example: eeb91fce-4be2-4a30-aad8-39e05fefde0
    .PARAMETER Credential
        Valid user credentials to Azure AD. The Azure AD user must
        have at least user rights in OMS and administrator and
        Contributor rights on the Azure resource group where
        the OMS workspace is located.
    .EXAMPLE
        $token = Get-AADToken -TenantADName 'stanoutlook.onmicrosoft.com' -Credential $creds
        Description
        -----------
        Grabs token from Azure AD by Tenant AD Name
        Example Variables
        -----------------
        $creds = Get-Credential

    .EXAMPLE
        $token = Get-AADToken -TenantID 'eeb91fce-4be2-4a30-aad8-39e05fefde0' -Credential $creds
        Description
        -----------
        Grabs token from Azure AD by Tenant ID
        Example Variables
        -----------------
        $creds = Get-Credential

    .EXAMPLE
        $Token = Get-AADToken -OMSConnection $OMSCon
        Description
        -----------
        Grabs token from Azure AD by using information from asset of type connection in OMS Automation
        Example Variables
        -----------------
        $OMSCon = Get-AutomationConnection -Name 'stasoutlook'

    .OUTPUTS
        System.String. Returns token from Azure AD.
#>
[CmdletBinding(DefaultParameterSetName='LoginbyTenantADName')]
[OutputType([string])]
PARAM (
        [Parameter(ParameterSetName='OMSConnection',Position=0,Mandatory=$true)]
        [Alias('Connection','c')]
        [Object]$OMSConnection,

        [Parameter(ParameterSetName='LoginbyTenantADName',Position=0,Mandatory=$true)]

        [Alias('t')]
        [String]$TenantADName,

        [Parameter(ParameterSetName='LoginByTenantID',Position=0,Mandatory=$true)]
        [ValidateScript({
            try
            {
                [System.Guid]::Parse($_) | Out-Null
                $true
            }
            catch
            {
                $false
            }
        })]
        [Alias('tID')]
        [String]$TenantID,

        [Parameter(ParameterSetName='LoginbyTenantADName',Position=1,Mandatory=$true)]
        [Parameter(ParameterSetName='LoginByTenantID',Position=1,Mandatory=$true)]
        [Alias('cred')]
        [pscredential]
        [System.Management.Automation.CredentialAttribute()]
        $Credential
        )
    Try
    {
        If ($OMSConnection)
        {
            $Username       = $OMSConnection.Username
            $Password       = $OMSConnection.Password
            If ($OMSConnection.TenantID)
            {
                $TenantID   = $OMSConnection.TenantID
            }
            Else
            {
                $TenantADName   = $OMSConnection.TenantADName
            }
        }
        Else
        {
            $Username       = $Credential.Username
            $Password       = $Credential.Password
        }
        # Set well-known client ID for Azure PowerShell
        $clientId = '1950a258-227b-4e31-a9cf-717495945fc2'

        # Set Resource URI to Azure Service Management API
        $resourceAppIdURI = 'https://management.azure.com/'

        # Set Authority to Azure AD Tenant
        If ($TenantID)
        {
            $authority = 'https://login.microsoftonline.com/common/' + $TenantID
        }
        Else
        {
            $authority = 'https://login.microsoftonline.com/' + $TenantADName
        }

        $AadModule = Get-Module -Name "AzureAD" -ListAvailable
        if ($AadModule.count -gt 1) {
            $Latest_Version = ($AadModule | Select-Object version | Sort-Object)[-1]
            $AadModule = $AadModule | Where-Object { $_.version -eq $Latest_Version.version }
        }

        $adal = Join-Path $AadModule.ModuleBase "Microsoft.IdentityModel.Clients.ActiveDirectory.dll"
        [System.Reflection.Assembly]::LoadFrom($adal) | Select-Object FullName

        $AADcredential = New-Object `
            -TypeName 'Microsoft.IdentityModel.Clients.ActiveDirectory.UserPasswordCredential' `
            -ArgumentList $Username,$Password

        # Create AuthenticationContext tied to Azure AD Tenant
        $authContext = New-Object `
            -TypeName 'Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContext' `
            -ArgumentList $authority

        $authResult = [Microsoft.IdentityModel.Clients.ActiveDirectory.AuthenticationContextIntegratedAuthExtensions]::AcquireTokenAsync($authContext, $resourceAppIdURI, $clientId, $AADcredential).Result

        $Token = $authResult.CreateAuthorizationHeader()
    }
    Catch
    {
        $ErrorMessage = 'Failed to aquire Azure AD token.'
        $ErrorMessage += " `n"
        $ErrorMessage += 'Error: '
        $ErrorMessage += $_
        Write-Error -Message $ErrorMessage `
                    -ErrorAction Stop
    }

    Return $Token
}