I realize this is old, but I figured I'd throw in the solution if you're using Python 3 with httplib2 since I haven't been able to find it anywhere else. I'm also authenticating against a Jenkins server using the API Token for each Jenkins user. If you're not concerned with Jenkins, simply substitute the actual user's password for the API Token.
b64encode is expecting an binary string of ASCII characters. With Python 3 a TypeError will be raised if a plain string is passed in. To get around this, the "user:api_token" portion of the header must be encoded using either 'ascii' or 'utf-8', passed to b64encode, then the resulting byte string must be decoded to a plain string before being placed in the header. The following code did what I needed:
import httplib2, base64
cred = base64.b64encode("{0}:{1}".format(
<user>, <api_token>).encode('utf-8')).decode()
headers = {'Authorization': "Basic %s" % cred}
h = httplib2.Http('.cache')
response, content = h.request("http://my.jenkins.server/job/my_job/enable",
"GET", headers=headers)