Unable to add authenticated "proxies" arg to protonmail Session

[twintersx]

Tried formats Host:Port:User:Pass and User:Pass@Host:Port
Has anyone else had any success with this?

proton_session = Session(
        'https://api.protonmail.ch',
        path.join(cwd, log_folder),
        path.join(cwd, "cache"),
        tls_pinning=False,
        proxies="Host:Port:Username:Password"
)
proton_session.authenticate(username=proton_email, password=proton_password)    #does not authenticate with proxy