Decode SAML Request or Response

Question

I am attempting to write a function to decode a SAML request or response. I'm missing something and can't seem to find the issue. I thought the issue was the encoding on the GetString but varying between UTF8, ASCII or Unicode doesn't seem to return the
xml string I am expecting.  Any suggestions.
function ConvertFromBase64{
 param($EncodedText
 Process{
  if($EnCodedText.contains("%")){
   $rawData = [System.Web.HttpUtility]::UrlDecode($EncodedText)
   $samlData = [System.Convert]::FromBase64String($rawData)
  else{
   $samlData = [System.Convert]::FromBase64String($EncodedText)
  [string] $DecodedText = [System.Text.Encoding]::UTF8.GetString($samlData)
  $DecodedText

Answer 1

Thanks for the information.  Unfortunately, that provides the same result I've been getting.  I've had some other people I know try it and they get the same result.  Below is the test I tried and the result.
function UrlDecode([string]$url) {
   [Web.Httputility]::UrlDecode($url)
function FromBase64([string]$str) {
   [text.encoding]::utf8.getstring([convert]::FromBase64String($str))
$text = "fZJNT%2BMwEIbvSPwHy%2Fd8tMvHympSdUGISuwS0cCBm%2BtMUwfbk%2FU4zfLvSVMq2Euv45n3fd7xzOb%2FrGE78KTRZXwSp5yBU1hpV2f8ubyLfvJ5fn42I2lNKxZd2Lon%2BNsBBTZMOhLjQ8Y77wRK0iSctEAiKLFa%2FH4Q0zgVrceACg1ny9uMy7rCdaM2%2Bs0BWrtppK2UAdeoVjW2ruq1bevGImcvR6zpHmtJ1MHSUZAuDKU0vY7Si2h6VU5%2BiMuJuLx65az4dPql3SHBKaz1oYnEfVkWUfG4KkeBna7A%2Fxm6M14j1gZihZazBRH4MODcoKPOgl%2BB32kFz08PGd%2BG0JJIkr7v46%2BhRCaEpod17DCRivYZCkmkd4N28B3wfNyrGKP5bws9DS6PKDz%2FMpsl36Tyz%2F%2Fax1jeFmi0emcLY7C%2F8SDD0Z7dobcynHbbV3QVbcZW0TlqQemNhoqzJD%2B4%2Fn8Yw7l8AA%3D%3D"
$Saml = UrlDecode $text
$Result = FromBase64 $Saml
$Result
I get.
}?MO?0►??H???|????jRuA?J?↕?????LS??8???IS*?K???}??????a;??e|↕???SXiWg????~?y~
~6#iM+▬]?'??☺♣6L:↕?C?;?♦J?$??@"(?Z?~►?8§?|
g????u?6??☺Z?i???☺?V5???m??"g/G??▲kI???Q?.♀?4???hzUN~?─??z??t???!?)?????}Y▬Q?*G
?????↓?3^#?♠b???♣◄?0????_??i♣?O☼↓??H????D&???u?0???↓
I?w?v?↔?|?↑??o♂=.?(<?2?%??????X?▬h?zg♂c??? ????2?v?Wt§m?V?9jA???$???⌂↑ù|