From bc601ae1ec724e2ba7e7fd51504529c4db245333 Mon Sep 17 00:00:00 2001
From: "Peter D. Gray" <peter@conalgo.com>
Date: Mon, 3 Jun 2024 11:03:01 -0400
Subject: [PATCH] add b2a_base64url

---
 shared/utils.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/shared/utils.py b/shared/utils.py
index f0d81c1f..e37c3a10 100644
--- a/shared/utils.py
+++ b/shared/utils.py
@@ -178,6 +178,10 @@ class Base64Writer:
             assert tmp[-2:-1] != b'=', tmp
             self.fd.write(tmp[:-1])
 
+def b2a_base64url(s):
+    # see <https://datatracker.ietf.org/doc/html/rfc4648#section-5>
+    return b2a_base64(s).rstrip(b'=\n').replace(b'+', b'-').replace(b'/', b'_')
+
 def swab32(n):
     # endian swap: 32 bits
     return ustruct.unpack('>I', ustruct.pack('<I', n))[0]