def expose_header(header, response):
    """
    Add a header name to Access-Control-Expose-Headers to allow client code to access that header's value
    """
    exposedHeaders = response.get('Access-Control-Expose-Headers', '')
    exposedHeaders += f', {header}' if exposedHeaders else header
    response['Access-Control-Expose-Headers'] = exposedHeaders
    return response