[libmicrohttpd] Digest authentication nonce uniqueness

[Ahmet Kermen]

Hi all,

Trying to implement digest authentication by following the sample code “digest_auth_example.c” from "https://git.gnunet.org/libmicrohttpd.git/tree/src/examples/digest_auth_example.c”.

For simple requests everything works fine without any issue.

When I try to send requests concurrently, some of them always fail, even two concurrent requests.

Still not sure exact reason why concurrent handling is not working, but at this point only clue I have for the issue appears to be “nonce” value of the authentication header being not unqiue for each (independent) request. This behaviour seems to be not compliant with RFC2617 https://datatracker.ietf.org/doc/html/rfc2617#section-3.2.1 and RFC7616 https://datatracker.ietf.org/doc/html/rfc7616#section-3.2 both state “nonce" values should be uniquely generated each time a 401 response is made while the values generated by libmicrohttpd are only unique for each second (by the “MHD_monotonic_sec_counter" function).

By the way the NONCE_NC_SIZE value is set to very large value to eliminate hash collisions.

When same concurrent test run with digest authentication implementation for popular frameworks (for Flask from https://flask-httpauth.readthedocs.io/en/latest, for Node.js from https://www.npmjs.com/package/http-auth, for httbin from https://hub.docker.com/r/kennethreitz/httpbin) they all seem to produce unique “nonce” values and handle concurrent requests wihtout any issue.

Please correct me If I’m wrong and missing something about the "nonce” value handling or it being source of the isssue.

Best regards,

Ahmet Kermen