SOCKS 5 username/password authentication doesn't exist?

I've been building a SOCKS 5 proxy from scratch and it was working perfectly fine when I redirected all my traffic through it with no authentication enabled. However, I noticed that adding credentials in my proxy settings did not actually do anything.

When I tried to use the username/password feature in the SOCKS proxy settings, I found after much debugging that the request contained x01 in the methods field (indicating it only supports 1 login method) and then that login method was x00 (NO AUTHENTICATION REQUIRED). Because of this, if my server requires a password, it is unable to agree on a connection method and fails to connect.

Output: \x05\x01\x00

If I did the connection manually via curl with my username and password, it would agree and connect.

Output: \x05\x03\x00\x01\x02

This means that curl supports 3 authentication methods: no authentication required, gssapi and username/password.

Certain mac services (i.e. cloudd) do support it and request a password to use the proxy (which works fine with these services), but the mac itself can't proxy requests through it.

Has anyone noticed something similar with SOCKS 5?