'Serialize as a header for an HTTPAuth request.'

def to_header(self, realm=''):

    auth_header = ('OAuth    realm="%s"' % realm)
    if self.parameters:
        for (k, v) in self.parameters.iteritems():
            if (k[:6] == 'oauth_'):
                auth_header += (',    %s="%s"' % (k, escape(str(v))))
    return {'Authorization': auth_header}
