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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _authenticate_user_dn(self, password):
 """ Binds to the LDAP server with the user's DN and password. Raises AuthenticationFailed on failure. """

        if self.dn is None:
            raise self.AuthenticationFailed("failed to map the username to a DN.")

        try:
            sticky = self.settings.BIND_AS_AUTHENTICATING_USER

            self._bind_as(self.dn, password, sticky=sticky)
        except ldap.INVALID_CREDENTIALS:
            raise self.AuthenticationFailed("user DN/password rejected by LDAP server.")