+`y` (byte array) \[uint8_t \*\*, size\_t \*\]
+
+: Convert an input string base64url encoded to its
+ byte array representation. The result and its length
+ are stored. The returned buffer must be freed by the caller.
+
+`Y` (byte array) \[uint8_t \*\*, size\_t \*\]
+
+: Like 'y' but input is base64.
+