Step 1
Create an account in the magentocommerce.com.
Step 2
Login to the magentocommerce.com.
Step 3
Switch to the «Connect» tab:
Step 4
Switch to the «Secure Keys» tab in the left sidebar, then specify an arbitrary secure key name in the «Name» input field, then press the «Generate new» button:
Step 5
You will see a «Public Key» and a «Private Key»:
I recommend to put these credentials into an auth.json file to skip typing the credentials during an authentication.