Pull out `twitter:` meta tags when generating a preview and
use it to augment any `og:` meta tags.

Prefers Open Graph information over Twitter card information.

Co-authored-by: David Robertson <david.m.robertson1@gmail.com>

Signed-off-by: Sean Quah <seanq@element.io>

* Rename test_fedclient to match its source file
* Require at least one destination to be truthy
* Explicitly validate user ID in profile endpoint GETs
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

Uniformize spam-checker API, part 4: port other spam-checker callbacks to return `Union[Allow, Codes]`. (#12857)

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

MSC3715 defines this parameter, but the unstable version of it should be
behind an experimental flag.

* Add tests for `/rooms/<room_id>/members` cancellation.
* Add tests for `/rooms/<room_id>/state` cancellation.

Signed-off-by: Sean Quah <seanq@element.io>

* Remove an unused stream ID generator.
* Remove the now unused remote profile cache.

Avoid breaking a URL preview completely if the chosen image 404s
or is unreachable for some other reason (e.g. DNS).

As opposed to only considering a user to have "participated" if they
replied to the thread.

* Skip `og` and `meta` tags where the value is empty.
* Fallback to the favicon if there are no other images.
* Ignore tags meant for navigation.

* Update worker docs to remove group endpoints.
* Removes an unused parameter to `ApplicationService`.
* Break dependency between media repo and groups.
* Avoid copying `m.room.related_groups` state events during room upgrades.

Signed-off-by: Nicolas Werner <nicolas.werner@hotmail.de>
Co-authored-by: Brendan Abolivier <github@brendanabolivier.com>

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

Instead of hard-coding strings in many places.

Add an option allowing users to use their password to reauthenticate even though password authentication is disabled. (#12883)

Makes it so that groups/communities no longer exist from a user-POV. E.g. we remove:

* All API endpoints (including Client-Server, Server-Server, and admin).
* Documented configuration options (and the experimental flag, which is now unused).
* Special handling during room upgrades.
* The `groups` section of the `/sync` response.

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

Parse the `m.relates_to` event content field (which describes relations)
in a single place, this is used during:

* Event persistence.
* Validation of the Client-Server API.
* Fetching bundled aggregations.
* Processing of push rules.

Each of these separately implement the logic and each made slightly
different assumptions about what was valid. Some had minor / potential
bugs.

* add Measure blocks all over SpamChecker

Signed-off-by: jesopo <github@lolnerd.net>

* fix test_spam_checker_may_join_room and test_threepid_invite_spamcheck

* better changelog entry

Co-authored-by: Matthew Hodgson <matthew@matrix.org>

Fixes a regression from 8b309adb (#11660)
and b65acead (#11752) where events which
themselves were an edit or an annotation could have bundled aggregations calculated,
which is not allowed.

* Changes hidden read receipts to be a separate receipt type
  (instead of a field on `m.read`).
* Updates the `/receipts` endpoint to accept `m.fully_read`.

* `m.login.jwt`, which was never specced and has been deprecated
  since Synapse 1.16.0. (`org.matrix.login.jwt` can be used instead.)
* `uk.half-shot.msc2778.login.application_service`, which was
  stabilized as part of the Matrix spec v1.2 release.

The `latest_event` field of the bundled aggregations for `m.thread` relations
did not include bundled aggregations itself. This resulted in clients needing to
immediately request the event from the server (and thus making it useless that
the latest event itself was serialized instead of just including an event ID).

When configuring the return values of mocks, prefer awaitables from
`make_awaitable` over `defer.succeed`. `Deferred`s are only awaitable
once, so it is inappropriate for a mock to return the same `Deferred`
multiple times.

Also update `run_in_background` to support functions that return
arbitrary awaitables.

Signed-off-by: Sean Quah <seanq@element.io>

* Corrects some typos / copy & paste errors in tests.
* Clarifies docstrings.
* Removes an unnecessary method.