code: public GSSCredential get(String username,
                               String passphrase,
                               int lifetime)
          throws MyProxyException {
          return get(null, username, passphrase, lifetime);
      }
docs: Retrieves delegated credentials from MyProxy server Anonymously
  (without local credentials)
  
  Notes: Performs simple verification of private/public keys of
  the delegated credential. Should be improved later.
  And only checks for RSA keys.
  
  @param  username
  The username of the credentials to retrieve.
  @param  passphrase
  The passphrase of the credentials to retrieve.
  @param  lifetime
  The requested lifetime of the retrieved credential (in seconds).
  @return GSSCredential
  The retrieved delegated credentials.
  @exception MyProxyException
  If an error occurred during the operation.