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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:

def __get_request_auth(username, password):
    '''
    Get libvirt.openAuth callback with username, password values overriding
    the configuration ones.
    '''

    # pylint: disable=unused-argument
    def __request_auth(credentials, user_data):
        '''Callback method passed to libvirt.openAuth().

        The credentials argument is a list of credentials that libvirt
        would like to request. An element of this list is a list containing
        5 items (4 inputs, 1 output):
          - the credential type, e.g. libvirt.VIR_CRED_AUTHNAME
          - a prompt to be displayed to the user
          - a challenge
          - a default result for the request
          - a place to store the actual result for the request

        The user_data argument is currently not set in the openAuth call.
        '''
        for credential in credentials:
            if credential[0] == libvirt.VIR_CRED_AUTHNAME:
                credential[4] = username if username else \
                                __salt__['config.get']('virt:connection:auth:username', credential[3])
            elif credential[0] == libvirt.VIR_CRED_NOECHOPROMPT:
                credential[4] = password if password else \
                                __salt__['config.get']('virt:connection:auth:password', credential[3])
            else:
                log.info('Unhandled credential type: %s', credential[0])
        return 0