It’s essentially just a wrapped regular API key/authorization header.
base64encode('Basic ' + base64encode('<access key>:<secret key>'))
Example:
access_key = 5D06A82B3A6C3BF2324E
secret_key = 5hYcESwP2LUzkTCLJMqsZgbyrregXUM7dFdsf8oJ
auth_header = 'Basic ' + base64(access_key + ':' + secret_key)
# NUQwNkE4MkIzQTZDM0JGMjMyNEU6NWhZY0VTd1AyTFV6a1RDTEpNcXNaZ2J5cnJlZ1hVTTdkRmRzZjhvSg==
token = base64(auth_header)
# QmFzaWMgTlVRd05rRTRNa0l6UVRaRE0wSkdNak15TkVVNk5XaFpZMFZUZDFBeVRGVjZhMVJEVEVwTmNYTmFaMko1Y25KbFoxaFZUVGRrUm1SelpqaHZTZz09