Encoding betfair API bot login details

[Phaedos]

I'm in the early stages of writing a bot for Betfair, and have got
the basics of logging in, getting prices etc down, but I am concerned about security of the login I am making. In the API-NG tutorial
(in the Certificate Login Interface Details section) they mention:

    Please note:  The username and password values should be encoded 
    when making the login request.

But what does that mean exactly, encoded how?

Currently I'm just following the tutorial Python example with:

payload = 'username=myusername&password=password'
headers = {'X-Application': 'SomeKey', 'Content-Type': 'application/x-www-form-urlencoded'}

resp = requests.post('https://identitysso.betfair.com/api/certlogin', data=payload,
cert=('client-2048.crt', 'client-2048.key'), headers=headers)

but does this mean my user and password are being sent insecurely?