fix(crypto): return client errors for malformed KMS contexts

Signed-off-by: Feng Ruohang <rh@vonng.com>

internal/crypto/sse-kms.go

@@ -76,9 +76,17 @@ func (ssekms) ParseHTTP(h http.Header) (string, kms.Context, error) {
 
 	var ctx kms.Context
 	if context, ok := h[xhttp.AmzServerSideEncryptionKmsContext]; ok {
+		invalidContext := kms.Error{
+			Code:    http.StatusBadRequest,
+			APICode: "InvalidArgument",
+			Err:     "KMS context must be valid base64-encoded JSON with string values",
+		}
+		if len(context) == 0 {
+			return "", nil, invalidContext
+		}
 		b, err := base64.StdEncoding.DecodeString(context[0])
 		if err != nil {
-			return "", nil, err
+			return "", nil, invalidContext
 		}
 		// Persisting invalid UTF-8 replaces bytes and can collapse distinct
 		// keys, changing the associated data needed to decrypt the object.
@@ -92,7 +100,7 @@ func (ssekms) ParseHTTP(h http.Header) (string, kms.Context, error) {
 
 		json := jsoniter.ConfigCompatibleWithStandardLibrary
 		if err := json.Unmarshal(b, &ctx); err != nil {
-			return "", nil, err
+			return "", nil, invalidContext
 		}
 	}