Ignore padding when decoding base64 data in wire protocol

The auth_client C library writes padded url-base64-encoded data.

codec.go

@@ -148,7 +148,7 @@ func (i *inputScanner) parseQuotedString() (string, error) {
 }
 
 func (i *inputScanner) parseBase64String() (string, error) {
-	data := i.parseUntilOrEOF(' ')
+	data := bytes.TrimRight(i.parseUntilOrEOF(' '), "=")
 	out := make([]byte, base64.RawURLEncoding.DecodedLen(len(data)))
 	_, err := base64.RawURLEncoding.Decode(out, data)
 	if err != nil {