binascii.Error: Invalid base64-encoded string (+workaround)

[Zydox]

Hello.

I'm using the HttpNegotiateAuth() function with requests to post a file to a kerberos SSO webserver and keept getting this error message in windows:
File "C:\Users\X.X\AppData\Roaming\Python\Python39\site-packages\requests_negotiate_sspi\requests_negotiate_sspi.py", line 149, in _retry_using_http_Negotiate_auth
tokenbuf.Buffer = base64.b64decode(final)
File "c:\Program Files\Python39\lib\base64.py", line 87, in b64decode
return binascii.a2b_base64(s)
binascii.Error: Invalid base64-encoded string: number of data characters (505) cannot be 1 more than a multiple of 4

I found that the final variable in the list:
tokenbuf.Buffer = base64.b64decode(final)
didn't contain a = character at the end, when I replaced the current like with this:
tokenbuf.Buffer = base64.b64decode(final + (b'=' if final[:-1] != '=' else b''))

After that, I didn't have any issues.

Best regards,
Zydox

[michael-o]

Can you share the Base64 string?