And convert some inlineDeferreds to async-friendly functions.

This breaks some people's configurations (if their Client-Server API
is not accessed via port 443).

This has the side-effect of being able to remove use of `inlineCallbacks`
in the test-cases for cleaner tracebacks.

* Handle the case of lxml not finding a document tree.
* Parse the document encoding from the XML tag.

Fixes some exceptions if the room state isn't quite as expected.
If the expected state events aren't found, try to find them in the
historical room state. If they still aren't found, fallback to a reasonable,
although ugly, value.

Also add a few more IP ranges to the default blacklist.

This could arguably replace the existing admin API for `/members`, however that is out of scope of this change.

This sort of endpoint is ideal for moderation use cases as well as other applications, such as needing to retrieve various bits of information about a room to perform a task (like syncing power levels between two places). This endpoint exposes nothing more than an admin would be able to access with a `select *` query on their database.

* Fixes a case where no summary text was returned.
* The use of messages_from_person vs. messages_from_person_and_others
  was tweaked to depend on whether there was 1 sender or multiple senders,
  not based on if there was 1 room or multiple rooms.

There's some prelimiary work here to pull out the construction of a jinja environment to a separate function.

I wanted to load the template at display time rather than load time, so that it's easy to update on the fly. Honestly, I think we should do this with all our templates: the risk of ending up with malformed templates is far outweighed by the improved turnaround time for an admin trying to update them.

Fixes #8966.

* Factor out build_synapse_client_resource_tree

Start a function which will mount resources common to all workers.

* Move sso init into build_synapse_client_resource_tree

... so that we don't have to do it for each worker

* Fix SSO-login-via-a-worker

Expose the SSO login endpoints on workers, like the documentation says.

* Update workers config for new endpoints

Add documentation for endpoints recently added (#8942, #9017, #9262)

* remove submit_token from workers endpoints list

this *doesn't* work on workers (yet).

* changelog

* Add a comment about the odd path for SAML2Resource

There are going to be a couple of paths to get to the final step of SSO reg, and I want the URL in the browser to consistent. So, let's move the final step onto a separate path, which we redirect to.

Signed-off-by: David Teller <davidt@element.io>

Fixes #8928.

Treat unknown encodings (according to lxml) as UTF-8
when generating a preview for HTML documents. This
isn't fully accurate, but will hopefully give a reasonable
title and summary.

This expands the current shadow-banning feature to be usable via
the admin API and adds documentation for it.

A shadow-banned users receives successful responses to their
client-server API requests, but the events are not propagated into rooms.

Shadow-banning a user should be used as a tool of last resort and may lead
to confusing or broken behaviour for the client.

Treat the content as untrusted and do not assume it is of
the proper form.

If no thumbnail of the requested type exists, return a 404 instead
of erroring. This doesn't quite match the spec (which does not define
what happens if no thumbnail can be found), but is consistent with
what Synapse already does.

... to avoid clashes with other SSO mechanisms

* Factor out a common TestHtmlParser

Looks like I'm doing this in a few different places.

* Improve OIDC login test

Complete the OIDC login flow, rather than giving up halfway through.

* Ensure that OIDC login works with multiple OIDC providers

* Fix bugs in handling clientRedirectUrl

 - don't drop duplicate query-params, or params with no value
 - allow utf-8 in query-params

0dd2649c (#9112) changed the signature of `auth_via_oidc`. Meanwhile,
26d10331 (#9091) introduced a new test which relied on the old signature of
`auth_via_oidc`. The two branches were never tested together until they landed
in develop.

We do this by allowing a single iteration to process multiple rooms at a
time, as there are often a lot of really tiny rooms, which can massively
slow things down.

This is the final step for supporting multiple OIDC providers concurrently.

First of all, we reorganise the config so that you can specify a list of OIDC providers, instead of a single one. Before:

    oidc_config:
       enabled: true
       issuer: "https://oidc_provider"
       # etc

After:

    oidc_providers:
     - idp_id: prov1
       issuer: "https://oidc_provider"

     - idp_id: prov2
       issuer: "https://another_oidc_provider"

The old format is still grandfathered in.

With that done, it's then simply a matter of having OidcHandler instantiate a new OidcProvider for each configured provider.

Protecting media stops it from being quarantined when
e.g. all media in a room is quarantined. This is useful
for sticker packs and other media that is uploaded by
server administrators, but used by many people.

Previously this code generated unreferenced `Deferred` instances
which caused "Unhandled Deferreds" errors to appear in error
situations.