Returns a DOFAuthenticator known to the DOF. 
- Parameters
 - 
  
    | self | The DOF. This must not be NULL.  | 
    | domainID | The domain ID. This should not be NULL. | 
  
   
- Returns
 - The DOFAuthenticator known to the DOF. 
 
- Exceptions
 - 
  
    | NULL | is returned if the authenticator is not known to the DOF, or an invalid parameter was detected.  |