Adding opentracing headers for appservice requests

[MTRNord]

Description:

Currently, synapse only sends the tracing span headers over federation (using the whitelist) and over replication. However, for appservice devs, it might also be nice to have the trace spans from synapse to follow the flow from the start instead of needing to manually find the right span.

For reference, I think it's probably just adding opentracing.inject_header_dict(headers, check_destination=False) somewhere in this area:

synapse/synapse/http/client.py

Line 562 in 93f2fdd

async def put_json(

or in

synapse/synapse/appservice/api.py

Lines 363 to 368 in 93f2fdd

	await self.put_json(
	f"{service.url}{APP_SERVICE_PREFIX}/transactions/{urllib.parse.quote(str(txn_id))}",
	json_body=body,
	args=args,
	headers={"Authorization": [f"Bearer {service.hs_token}"]},
	)

However, I didn't work on the synapse codebase so far. So the pointers may not be accurate.

[clokep]

Seems like a good idea, would be great to have a PR adding this.

[MTRNord]

Seems like a good idea, would be great to have a PR adding this.

I will see how my weekend plays out and do that. I am coming from actually having somewhat a need for this :) So I guess I can learn how to do a synapse PR :) This seems like a rather small change.