def update_chap_credentials(TargetARN=None, SecretToAuthenticateInitiator=
    None, InitiatorName=None, SecretToAuthenticateTarget=None):
    """
    Updates the Challenge-Handshake Authentication Protocol (CHAP) credentials for a specified iSCSI target. By default, a gateway does not have CHAP enabled; however, for added security, you might use it.
    See also: AWS API Documentation
    
    Examples
    Updates the Challenge-Handshake Authentication Protocol (CHAP) credentials for a specified iSCSI target.
    Expected Output:
    
    :example: response = client.update_chap_credentials(
        TargetARN='string',
        SecretToAuthenticateInitiator='string',
        InitiatorName='string',
        SecretToAuthenticateTarget='string'
    )
    
    
    :type TargetARN: string
    :param TargetARN: [REQUIRED]
            The Amazon Resource Name (ARN) of the iSCSI volume target. Use the DescribeStorediSCSIVolumes operation to return the TargetARN for specified VolumeARN.
            

    :type SecretToAuthenticateInitiator: string
    :param SecretToAuthenticateInitiator: [REQUIRED]
            The secret key that the initiator (for example, the Windows client) must provide to participate in mutual CHAP with the target.
            Note
            The secret key must be between 12 and 16 bytes when encoded in UTF-8.
            

    :type InitiatorName: string
    :param InitiatorName: [REQUIRED]
            The iSCSI initiator that connects to the target.
            

    :type SecretToAuthenticateTarget: string
    :param SecretToAuthenticateTarget: The secret key that the target must provide to participate in mutual CHAP with the initiator (e.g. Windows client).
            Byte constraints: Minimum bytes of 12. Maximum bytes of 16.
            Note
            The secret key must be between 12 and 16 bytes when encoded in UTF-8.
            

    :rtype: dict
    :return: {
        'TargetARN': 'string',
        'InitiatorName': 'string'
    }
    
    
    """
    pass
