How to use the instana.singletons.agent.extra_headers function in instana

def test_client_response_header_capture(self):
        original_extra_headers = agent.extra_headers
        agent.extra_headers = ['X-Capture-This']

        async def test():
            with async_tracer.start_active_span('test'):
                async with aiohttp.ClientSession() as session:
                    return await self.fetch(session, testenv["wsgi_server"] + "/response_headers")

        response = self.loop.run_until_complete(test())

        spans = self.recorder.queued_spans()
        self.assertEqual(3, len(spans))

        wsgi_span = spans[0]
        aiohttp_span = spans[1]
        test_span = spans[2]

def test_client_response_header_capture(self):
        original_extra_headers = agent.extra_headers
        agent.extra_headers = ['X-Capture-This']

        async def test():
            with async_tracer.start_active_span('test'):
                async with aiohttp.ClientSession() as session:
                    return await self.fetch(session, testenv["wsgi_server"] + "/response_headers")

        response = self.loop.run_until_complete(test())

        spans = self.recorder.queued_spans()
        self.assertEqual(3, len(spans))

        wsgi_span = spans[0]
        aiohttp_span = spans[1]
        test_span = spans[2]

        self.assertIsNone(async_tracer.active_span)

def test_response_header_capture(self):
        original_extra_headers = agent.extra_headers
        agent.extra_headers = ['X-Capture-This']

        with tracer.start_active_span('test'):
            r = self.http.request('GET', testenv["wsgi_server"] + '/response_headers')

        spans = self.recorder.queued_spans()
        self.assertEqual(3, len(spans))

        wsgi_span = spans[0]
        urllib3_span = spans[1]
        test_span = spans[2]

        assert(r)
        self.assertEqual(200, r.status)
        self.assertIsNone(tracer.active_span)

        # Same traceId

res = start_response(status, headers, exc_info)

                sc = status.split(' ')[0]
                if 500 <= int(sc) <= 511:
                    scope.span.mark_as_errored()

                scope.span.set_tag(tags.HTTP_STATUS_CODE, sc)
                scope.close()
                return res
            else:
                return start_response(status, headers, exc_info)

        ctx = tracer.extract(ot.Format.HTTP_HEADERS, env)
        scope = env['stan_scope'] = tracer.start_active_span("wsgi", child_of=ctx)

        if hasattr(agent, 'extra_headers') and agent.extra_headers is not None:
            for custom_header in agent.extra_headers:
                # Headers are available in this format: HTTP_X_CAPTURE_THIS
                wsgi_header = ('HTTP_' + custom_header.upper()).replace('-', '_')
                if wsgi_header in env:
                    scope.span.set_tag("http.%s" % custom_header, env[wsgi_header])

        if 'PATH_INFO' in env:
            scope.span.set_tag('http.path', env['PATH_INFO'])
        if 'QUERY_STRING' in env and len(env['QUERY_STRING']):
            scrubbed_params = strip_secrets(env['QUERY_STRING'], agent.secrets_matcher, agent.secrets_list)
            scope.span.set_tag("http.params", scrubbed_params)
        if 'REQUEST_METHOD' in env:
            scope.span.set_tag(tags.HTTP_METHOD, env['REQUEST_METHOD'])
        if 'HTTP_HOST' in env:
            scope.span.set_tag("http.host", env['HTTP_HOST'])

ctx = tornado_tracer.extract(opentracing.Format.HTTP_HEADERS, instance.request.headers)
                    scope = tornado_tracer.start_active_span('tornado-server', child_of=ctx)

                    # Query param scrubbing
                    if instance.request.query is not None and len(instance.request.query) > 0:
                        cleaned_qp = strip_secrets(instance.request.query, agent.secrets_matcher, agent.secrets_list)
                        scope.span.set_tag("http.params", cleaned_qp)

                    url = "%s://%s%s" % (instance.request.protocol, instance.request.host, instance.request.path)
                    scope.span.set_tag("http.url", url)
                    scope.span.set_tag("http.method", instance.request.method)

                    scope.span.set_tag("handler", instance.__class__.__name__)

                    # Custom header tracking support
                    if hasattr(agent, 'extra_headers') and agent.extra_headers is not None:
                        for custom_header in agent.extra_headers:
                            if custom_header in instance.request.headers:
                                scope.span.set_tag("http.%s" % custom_header, instance.request.headers[custom_header])

                    setattr(instance.request, "_instana", scope)

                    # Set the context response headers now because tornado doesn't give us a better option to do so
                    # later for this request.
                    tornado_tracer.inject(scope.span.context, opentracing.Format.HTTP_HEADERS, instance._headers)
                    instance.set_header(name='Server-Timing', value="intid;desc=%s" % scope.span.context.trace_id)

                    return wrapped(*argv, **kwargs)
            except Exception:
                logger.debug("tornado execute", exc_info=True)

async def stan_request_end(session, trace_config_ctx, params):
        try:
            scope = trace_config_ctx.scope
            if scope is not None:
                scope.span.set_tag('http.status_code', params.response.status)

                if hasattr(agent, 'extra_headers') and agent.extra_headers is not None:
                    for custom_header in agent.extra_headers:
                        if custom_header in params.response.headers:
                            scope.span.set_tag("http.%s" % custom_header, params.response.headers[custom_header])

                if 500 <= params.response.status <= 599:
                    scope.span.mark_as_errored({"http.error": params.response.reason})

                scope.close()
        except Exception:
            logger.debug("stan_request_end", exc_info=True)

def collect_response(scope, response):
        try:
            scope.span.set_tag(ext.HTTP_STATUS_CODE, response.status)

            if hasattr(agent, 'extra_headers') and agent.extra_headers is not None:
                for custom_header in agent.extra_headers:
                    if custom_header in response.headers:
                        scope.span.set_tag("http.%s" % custom_header, response.headers[custom_header])

            if 500 <= response.status <= 599:
                scope.span.mark_as_errored()
        except Exception:
            logger.debug("collect_response", exc_info=True)

scope = tornado_tracer.start_active_span('tornado-server', child_of=ctx)

                    # Query param scrubbing
                    if instance.request.query is not None and len(instance.request.query) > 0:
                        cleaned_qp = strip_secrets(instance.request.query, agent.secrets_matcher, agent.secrets_list)
                        scope.span.set_tag("http.params", cleaned_qp)

                    url = "%s://%s%s" % (instance.request.protocol, instance.request.host, instance.request.path)
                    scope.span.set_tag("http.url", url)
                    scope.span.set_tag("http.method", instance.request.method)

                    scope.span.set_tag("handler", instance.__class__.__name__)

                    # Custom header tracking support
                    if hasattr(agent, 'extra_headers') and agent.extra_headers is not None:
                        for custom_header in agent.extra_headers:
                            if custom_header in instance.request.headers:
                                scope.span.set_tag("http.%s" % custom_header, instance.request.headers[custom_header])

                    setattr(instance.request, "_instana", scope)

                    # Set the context response headers now because tornado doesn't give us a better option to do so
                    # later for this request.
                    tornado_tracer.inject(scope.span.context, opentracing.Format.HTTP_HEADERS, instance._headers)
                    instance.set_header(name='Server-Timing', value="intid;desc=%s" % scope.span.context.trace_id)

                    return wrapped(*argv, **kwargs)
            except Exception:
                logger.debug("tornado execute", exc_info=True)

def before_request_with_instana(*argv, **kwargs):
    try:
        env = flask.request.environ
        ctx = None

        if 'HTTP_X_INSTANA_T' in env and 'HTTP_X_INSTANA_S' in env:
            ctx = tracer.extract(opentracing.Format.HTTP_HEADERS, env)

        flask.g.scope = tracer.start_active_span('wsgi', child_of=ctx)
        span = flask.g.scope.span

        if hasattr(agent, 'extra_headers') and agent.extra_headers is not None:
            for custom_header in agent.extra_headers:
                # Headers are available in this format: HTTP_X_CAPTURE_THIS
                header = ('HTTP_' + custom_header.upper()).replace('-', '_')
                if header in env:
                    span.set_tag("http.%s" % custom_header, env[header])

        span.set_tag(ext.HTTP_METHOD, flask.request.method)
        if 'PATH_INFO' in env:
            span.set_tag(ext.HTTP_URL, env['PATH_INFO'])
        if 'QUERY_STRING' in env and len(env['QUERY_STRING']):
            scrubbed_params = strip_secrets(env['QUERY_STRING'], agent.secrets_matcher, agent.secrets_list)
            span.set_tag("http.params", scrubbed_params)
        if 'HTTP_HOST' in env:
            span.set_tag("http.host", env['HTTP_HOST'])

        if hasattr(flask.request.url_rule, 'rule') and \
                path_tpl_re.search(flask.request.url_rule.rule) is not None: