There was issue reported, which is closed with bad results.

Don't pass unicode strings in the arguments, but use UTF8 bytes instead.

self.session.get(main_url, auth=requests.auth.HTTPDigestAuth("Сергей_Ласточкин".encode('UTF-8'), '1234'))

Originally posted by @D-stefaang in #5089 (comment)

But this is wrong! When i try to set user 'Ondřej' with this advice, requests send bad string:

HTTPDigestAuth('Ondřej'.encode('utf-8'), 'heslíčko')

creates header starts with wrong username!

Digest username="b'Ond\xc5\x99ej'"