internal/functions/resolve/Resolve-Subscription.ps1

function Resolve-Subscription {
    [CmdletBinding()]
    Param (
        [Parameter(Mandatory = $true)]
        [string] $InputReference,
        [switch] $Expand, # Return object { id, displayName }
        [switch] $DisplayName,
        [System.Management.Automation.PSCmdlet]
        $Cmdlet = $PSCmdlet
    )

    begin {
        $InputReference = Resolve-String -Text $InputReference
        $token = (Get-AzAccessToken -ResourceUrl $script:apiBaseUrl).Token
        if ($token.GetType().Name -eq "SecureString") {
            $bstr = [System.Runtime.InteropServices.Marshal]::SecureStringToBSTR($token)
            $token = [System.Runtime.InteropServices.Marshal]::PtrToStringAuto($bstr)
        }
    }
    process
    {            
        try {
            $subs = (Invoke-RestMethod -Method GET -uri "$($script:apiBaseUrl)subscriptions?$($script:apiVersion)" -Headers @{"Authorization"="Bearer $($token)"}).value
            $match = if ($InputReference -match $script:guidRegex) { $subs | Where-Object { $_.subscriptionId -eq $InputReference } | Select-Object -First 1 } else { $subs | Where-Object { $_.displayName -eq $InputReference } | Select-Object -First 1 }
            if (-not $match) { throw "Can not find subscription $InputReference" }
            if (-not $Expand) { if ($DisplayName) { return ($match.displayName) } return $match.id }
            return [pscustomobject]@{ id=$match.id; displayName=$match.displayName; subscriptionId=$match.subscriptionId }
        }
        catch {
            Write-PSFMessage -Level Warning -Message ("Cannot resolve Subscription resource for input '{0}'. Searched tenant & desired configuration. Error: {1}" -f $InputReference,$_.Exception.Message) -Tag 'failed' -ErrorRecord $_
            $Cmdlet.ThrowTerminatingError($_)
        }
    }
}