Fix non-ascii characters in SAML Response

[restena-pyg]

• decode_base64 function may produce inadequate characters from non-ascii base64 encoded characters. utf8::decode helps fixing these characters.
• Digest calculation may differ from the digest within SAML response for non-ascii characters. utf8::encode allows ..._base64 functions to calculate a correct digest.
• Root cause: digest algorithms operate on sequences of bytes while inputs can be strings (so potentially wide charecters). More info on https://perldoc.perl.org/Digest::SHA#UNICODE-AND-SIDE-EFFECTS