Format oneline PEM private key to multiline format.

FormatPem.ps1

param(
    [Parameter(Mandatory=$true, Position=0, ValueFromPipeline=$false)]
    [string]
    $privateKey,

    [Parameter(Mandatory=$false, Position=1, ValueFromPipeline=$false)]
    [string]
    $delim = "\r\n"
)

#Set-PSDebug -Trace 1

$header="-----BEGIN PRIVATE KEY-----"
$footer="-----END PRIVATE KEY-----"
$charPerLine = 64

$newLineCount = [math]::Ceiling($privateKey.Length/$charPerLine) + 1
$privateKeyFormatted = $privateKey
$arr = @(1..$newLineCount)

# Character limit of 100
#$pattern = "(\w{" + $newLineCount + "})"
#$privateKey -split $pattern | ? {$_}

$prev = 0
$cur = ($charPerLine - 1)
$keyArr = @($null) * $newLineCount
foreach ($i in $arr) {
	if ($i -eq $newLineCount-1) {
		$keyArr[$i] = $privateKey.Substring($prev, $privateKey.Length - $prev)
		break
	}
	
	$keyArr[$i] = $privateKey.Substring($prev, $charPerLine)
	$prev = $cur
	$cur += $charPerLine
}

$privateKeyFormatted = $header
$privateKeyFormatted += $keyArr -join $delim
$privateKeyFormatted += $delim + $footer 
$privateKeyFormatted