SAML XML is always parsed assuming utf-8 encoding

[ziluvatar]

While reading the SAMLRequest the library converts the base64 string to a Buffer, after that it converts whether to a string without considering if the XML defined a different encoding in the prolog:

<?xml version="1.0" encoding="UTF-8" ?> <== usually UTF-8 is used, in some cases it can contain a different encoding. We should read the rest of XML based on that encoding.