Get-WpmRestApp.ps1

function Get-WpmRestApp {
    [CmdletBinding()]

    Param (

        [Parameter(
            Position = 0,
            ValuefromPipelineByPropertyName = $true,
            ValuefromPipeline = $true,
            Mandatory = $true
        )]
        [Alias('Id')]
        [System.String]$PackageIdentifier,

        [Parameter(
            ValuefromPipelineByPropertyName = $true
        )]
        [System.Uri]$Uri = 'https://pkgmgr-wgrest-pme.azurefd.net/api/packageManifests/',

        [Parameter(
            ValuefromPipelineByPropertyName = $true
        )]
        [Int]$ApiTimeoutSeconds = 90
    )

    begin {
        Set-StrictMode -Version Latest
    } # begin
    process {

        Write-Verbose "Querying $PackageIdentifier from $Uri"

        $queryUri = $Uri.ToString().TrimEnd('/') + '/' + $PackageIdentifier

        $noResponse = $true
        $timeSpan = (Get-Date).AddSeconds($ApiTimeoutSeconds)
        while ($noResponse) {
            if ((Get-Date) -gt $timeSpan) {
                Write-Error "Timeout waiting for $PackageIdentifier response from $queryUri"
                return
            }
            try {
                $package = Invoke-RestMethod -Uri $queryUri -ErrorAction Stop
                $noResponse = $false
            }
            catch {
                Start-Sleep -Milliseconds 500
            }
        }

        if ($null -eq $package) {
            Write-Error "Could not find package with Id $PackIdentifier"
            return
        }

        try {
            $packageNewest = $package.Data.Versions | Select-Object @{Name = 'PackageVersion'; Expression = { [Version]$_.PackageVersion } }, Installers, DefaultLocale
            if (($packageNewest.PackageVersion | Measure-Object).Count -eq 0) {
                $packageNewest = $package.Data.Versions | Select-Object  @{Name = 'PackageVersion'; Expression = { 
                        $_.PackageVersion -match "(\D{0})(\d+)((\.{1}\d+)*)(\.{0})" | Out-Null
                        if ($($Matches[0]) -notlike "*.*") { 
                            [Version]($Matches[0] + ".0") 
                        } 
                        else {
                            [Version]$Matches[0] 
                        } 
                    }
                } , Installers, DefaultLocale
            }
        }
        catch {
            Write-Output $_
        }

        $packageDetail = $packageNewest | Sort-Object -Property PackageVersion -Descending | Select-Object -First 1

        $timeSpan = (Get-Date).AddSeconds(30)
        $appInfo = $null
        while (($appInfo | Measure-Object).Count -eq 0 ) {
            if ((Get-Date) -gt $timeSpan) {
                Write-Error "Timeout waiting for version query match for $PackIdentifier"
                return
            }
            $appInfo = $package.Data.versions | Where-Object { -join $_.Installers.InstallerSha256 -eq -join $packageDetail.Installers.InstallerSha256 }
        }
        
        foreach ($installer in $packageDetail.Installers) {

            $output = [PSCustomObject]@{
                PackageName               = $package.Data.PackageIdentifier
                PackageVersion            = $packageDetail.PackageVersion
                Publisher                 = $appInfo.DefaultLocale.Publisher
                ShortDescription          = $appInfo.DefaultLocale.ShortDescription
                InstallerIdentifier       = $installer.InstallerIdentifier      
                InstallerSha256           = $installer.InstallerSha256
                InstallerUrl              = $installer.InstallerUrl
                Architecture              = $installer.Architecture
                InstallerType             = $installer.InstallerType
                Scope                     = if ($installer.PSobject.Properties.Name -contains 'Scope') { $installer.Scope } else { $null }
                InstallerSwitches         = if ($installer.PSobject.Properties.Name -contains 'InstallerSwitches') { $installer.InstallerSwitches } else { $null }
                Commands                  = if ($installer.PSobject.Properties.Name -contains 'Commands') { $installer.Commands } else { $null }
                InstallerAbortsTerminal   = $installer.InstallerAbortsTerminal
                ReleaseDate               = $installer.ReleaseDate
                InstallLocationRequired   = $installer.InstallLocationRequired
                RequireExplicitUpgrade    = $installer.RequireExplicitUpgrade
                DisplayInstallWarnings    = $installer.DisplayInstallWarnings
                DownloadCommandProhibited = $installer.DownloadCommandProhibited
            }

            Write-Output $output
        }

    } # process
    end {} # end

}  #function

Is the new REST API ready for public use?

@pl4nty this API isn't publicly supported no.