human
Solve the following python programming problem given the following code:
def test_custom_authorisation(self) : 
    SilkyConfig ().SILKY_AUTHENTICATION = True 
    SilkyConfig ().SILKY_AUTHORISATION = True 
    def custom_authorisation(user) : 
        return user.username.startswith ('mike') 
SilkyConfig ().SILKY_PERMISSIONS = custom_authorisation 
    username_and_password = 'bob' 
    user = User.objects.create (username = username_and_password) 
    user.set_password (username_and_password) 
    user.save () 
    self.client.login (username = <MASK>, password = username_and_password) 
    response = self.client.get (silky_reverse ('requests')) 
    self.assertEqual (response.status_code, 403) 
    user.username = 'mike2' 
    user.save () 
    response = self.client.get (silky_reverse ('requests')) 
    self.assertEqual (response.status_code, 200) 
    
    Given the code above, what is a proper replacement for <MASK>? Choose among: response, username_and_password, self, custom_authorisation, user
assistant
#Here is a proper replacement for <MASK>.
username_and_password