@PipelineProperty(description = "Comma delimited list of stream meta data keys to include as HTTP headers. " +
                                    "Only works when httpHeadersIncludeStreamMetaData is set to true. If empty all " +
                                    "headers are sent, unless httpHeadersStreamMetaDataDenyList is used. " +
                                    "If httpHeadersStreamMetaDataAllowList contains keys, " +
                                    "httpHeadersStreamMetaDataDenyList is ignored.",
            defaultValue = "",
            displayPriority = 27)
    public void setHttpHeadersStreamMetaDataAllowList(final String newValue) {
        this.httpHeadersStreamMetaDataAllowList = newValue;
    }
Handler class that forwards the request to a URL.
stroom-pipeline/src/main/java/stroom/pipeline/writer/HTTPAppender.java