def parse_header(field):
    """Parses a single header key and converts it to the way it appears on a HTTP classified_request.
    This function is necessary because the headers' keys are provided in the environment variables
    not as they appear in a HTTP classified_request.
    For example, it converts HTTP_USER_AGENT to User-Agent."""
    header_key = field[5:]  # Gets rid of the "HTTP_" prefix of the field.
    header_list = header_key.split("_")
    header_list = [string.capitalize() for string in header_list]
    return "-".join(header_list)