[utils] Add `jwt_decode_hs256`

Code from #1340
Authored by: Ashish0804

yt_dlp/utils.py

@@ -6512,6 +6512,13 @@ def jwt_encode_hs256(payload_data, key, headers={}):
     return token
 
 
+# can be extended in future to verify the signature and parse header and return the algorithm used if it's not HS256
+def jwt_decode_hs256(jwt):
+    header_b64, payload_b64, signature_b64 = jwt.split('.')
+    payload_data = json.loads(base64.urlsafe_b64decode(payload_b64))
+    return payload_data
+
+
 def supports_terminal_sequences(stream):
     if compat_os_name == 'nt':
         if get_windows_version() < (10, 0, 10586):