Getting 401 on Twitter OAuth POST requests

Question

I am trying to use Twitter OAuth and my POST requests are failing with a 401 (Invalid OAuth Request) error.

For example, if I

Answer 1

I second the answer by Jrgns. I has exactly the same issue. When reading the example Twitter provides, it's actually clear. However their pseudo code is misleading. In Python this worked for me :

def encodekeyval(key, val):
    key = urllib.quote(key, '')
    val = urllib.quote(val, '')
    return urllib.quote(key + '=' + val, '')

def signature_base_string(urlstr, oauthdata):
    sigstr = 'POST&' + urllib.quote(urlstr,'') + '&'
    # retrieve "post" data as dictionary of name value pairs
    pdata = oauthdata.getpdata()
    # need to sort parameters
    pstr = '%26'.join([encodekeyval(key, pdata[key]) for key in sorted(pdata.keys())])
    return sigstr + pstr