// Decode nonce from Base64
// format of nonce is
// base64(expirationTime + "" + md5Hex(expirationTime + "" + key))
String plainTextNonce = new String( Base64.decodeBase64( auth.getNonce().getBytes() ) );
NonceValidity validity = nonceProvider.getNonceValidity( plainTextNonce, nc );
if( NonceValidity.INVALID.equals( validity ) ) {
log.debug( "invalid nonce: " + plainTextNonce );
return null;
} else if( NonceValidity.EXPIRED.equals( validity ) ) {
log.debug( "expired nonce: " + plainTextNonce );