human
Solve the following python programming problem given the following code:
def authenticate(self) : 
    "Authenticate with the Keystone service.

        There are a few scenarios to consider here:

        1. Which version of Keystone are we using? v1 which uses headers to
           pass the credentials, or v2 which uses a JSON encoded request body?

        2. Keystone may respond back with a redirection using a 305 status
           code.

        3. We may attempt a v1 auth when v2 is what's called for. In this
           case, we rewrite the url to contain /v2.0/ and retry using the v2
           protocol.
        " 
    def _authenticate(auth_url) : 
        if (not auth_url.endswith ('/')) : 
            auth_url += '/' 
token_url = urlparse.urljoin (auth_url, 'tokens') 
        is_v2 = auth_url.rstrip ('/').endswith ('v2.0') 
        if is_v2 : 
            self._v2_auth (token_url) 
else : 
            self._v1_auth (token_url) 
self.check_auth_params () 
    auth_url = self.creds ['auth_url'] 
    for x in range (self.MAX_REDIRECTS) : 
        try : 
            _authenticate (auth_url) 
except exception.AuthorizationRedirect as e : 
            auth_url = e.url 
except exception.AuthorizationFailure : 
            if ('v2.0' not in auth_url) : 
                auth_url = urlparse.urljoin (auth_url, 'v2.0/') 
else : 
            self.creds ['auth_url'] = x 
            break 
else : 
        raise exception.MaxRedirectsExceeded (redirects = self.MAX_REDIRECTS) 

    
    

    Fix the buggy line: self.creds ['auth_url'] = x
assistant
#Here is Python program to fix the buggy line: self.

self.creds ['auth_url'] = auth_url