def client_authenticator_factory(mechanism):
authenticator = CLIENT_MECHANISMS_D[mechanism]<EOL>return authenticator()<EOL>
Create a client authenticator object for given SASL mechanism.

    :Parameters:
        - `mechanism`: name of the SASL mechanism ("PLAIN", "DIGEST-MD5" or
          "GSSAPI").
    :Types:
        - `mechanism`: `unicode`

    :raises `KeyError`: if no client authenticator is available for this
              mechanism

    :return: new authenticator.
    :returntype: `sasl.core.ClientAuthenticator`