v0.4.0 harden jwt, scram, credential handling, remove legacy adapters

encoding.go

@@ -0,0 +1,23 @@
+package auth
+
+import (
+	"encoding/base64"
+	"errors"
+	"strings"
+)
+
+// Bound allocation before decoding and reject non-canonical encodings, including
+// CR/LF (which encoding/base64 accepts even in Strict mode).
+func decodeBase64(s string, encoding *base64.Encoding, maxBytes int) ([]byte, error) {
+	if len(s) > encoding.EncodedLen(maxBytes) || strings.ContainsAny(s, "\r\n") {
+		return nil, errors.New("invalid base64 length or whitespace")
+	}
+	b, err := encoding.Strict().DecodeString(s)
+	if err != nil {
+		return nil, err
+	}
+	if len(b) > maxBytes {
+		return nil, errors.New("decoded value exceeds limit")
+	}
+	return b, nil
+}