sigv2: Unespace canonicalized resources values (#4034)

Values of canonicalized query resources should be unescaped before calculating
the signature. This bug is not noticed before because partNumber and uploadID
values in Minio doesn't have characters that need to be escaped.

cmd/signature-v2.go

@@ -282,7 +282,13 @@ func canonicalizedResourceV2(encodedPath string, encodedQuery string) string {
 			canonicalQueries = append(canonicalQueries, key)
 			continue
 		}
-		canonicalQueries = append(canonicalQueries, key+"="+val)
+		// Resources values should be unescaped
+		unescapedVal, err := url.QueryUnescape(val)
+		if err != nil {
+			errorIf(err, "Unable to unescape query value (query = `%s`, value = `%s`)", key, val)
+			continue
+		}
+		canonicalQueries = append(canonicalQueries, key+"="+unescapedVal)
 	}
 	if len(canonicalQueries) == 0 {
 		return encodedPath