def server_authenticator_factory(mechanism, password_database):
authenticator = SERVER_MECHANISMS_D[mechanism]<EOL>return authenticator(password_database)<EOL>
Create a server authenticator object for given SASL mechanism and
    password databaser.

    :Parameters:
        - `mechanism`: name of the SASL mechanism ("PLAIN", "DIGEST-MD5" or "GSSAPI").
        - `password_database`: name of the password database object to be used
          for authentication credentials verification.
    :Types:
        - `mechanism`: `str`
        - `password_database`: `PasswordDatabase`

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

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