'Returns a URL with an encoded OpenID request.
The resulting URL is the OpenID provider\'s endpoint URL with
parameters appended as query arguments.  You should redirect
the user agent to this URL.
OpenID 2.0 endpoints also accept POST requests, see
C{L{shouldSendRedirect}} and C{L{formMarkup}}.
@param realm: The URL (or URL pattern) that identifies your
web site to the user when she is authorizing it.
@type realm: str
@param return_to: The URL that the OpenID provider will send the
user back to after attempting to verify her identity.
Not specifying a return_to URL means that the user will not
be returned to the site issuing the request upon its
completion.
@type return_to: str
@param immediate: If True, the OpenID provider is to send back
a response immediately, useful for behind-the-scenes
authentication attempts.  Otherwise the OpenID provider
may engage the user before providing a response.  This is
the default case, as the user may need to provide
credentials or approve the request before a positive
response can be sent.
@type immediate: bool
@returns: The URL to redirect the user agent to.
@returntype: str'

def redirectURL(self, realm, return_to=None, immediate=False):

    message = self.getMessage(realm, return_to, immediate)
    return message.toURL(self.endpoint.server_url)
