Currently `DeviceMessageHandler` only ever exists on master, but that is about to change.

Signed-off-by: Emelie <em@nao.sh>

This allows for efficiently finding which users ignore a particular
user.

Co-authored-by: Erik Johnston <erik@matrix.org>

... for running the tests with no optional deps.

If we are lacking an optional dependency, skip the tests that rely on it.

This can happen when using a split out state database and we've upgraded
the schema version without there being any changes in the state schema.

These may be omitted if not set, but Synapse assumed they would
be in the response.

The last stream token is always known and we do not need to handle none.

Ex.

 - homeserver.log.2020-12-29
 - homeserver.log.2020-12-31

An experimental room version ("org.matrix.msc2176") contains
the new redaction rules for testing.

During login, if there are multiple IdPs enabled, offer the user a choice of
IdPs.

* Implement CasHandler.handle_redirect_request

... to make it match OidcHandler and SamlHandler

* Clean up interface for OidcHandler.handle_redirect_request

Make it accept `client_redirect_url=None`.

* Clean up interface for `SamlHandler.handle_redirect_request`

... bring it into line with CAS and OIDC by making it take a Request parameter,
move the magic for `client_redirect_url` for UIA into the handler, and fix the
return type to be a `str` rather than a `bytes`.

* Define a common protocol for SSO auth provider impls

* Give SsoIdentityProvider an ID and register them

* Combine the SSO Redirect servlets

Now that the SsoHandler knows about the identity providers, we can combine the
various *RedirectServlets into a single implementation which delegates to the
right IdP.

* changelog

The `RoomDirectoryFederationTests` tests were not being run unless explicitly called as an `__init__.py` file was not present in `tests/federation/transport/`. Thus the folder was not a python module, and `trial` did not look inside for any test cases to run. This was found while working on #6739.

This PR adds a `__init__.py` and also fixes the test in a couple ways:

- Switch to subclassing `unittest.FederatingHomeserverTestCase` instead, which sets up federation endpoints for us.
- Supply a `federation_auth_origin` to `make_request` in order to more act like the request is coming from another server, instead of just an unauthenicated client requesting a federation endpoint.

I found that the second point makes no difference to the test passing, but felt like the right thing to do if we're testing over federation.

This makes the "messages" key in the content required. This is currently
optional in the spec, but that seems to be an error.

Removes the trailing slash with causes issues with matrix.to/Element.

Adds the redacts endpoint to workers that have the client listener.

This table has been unused since Synapse v1.17.0.

Tests were broken due to an API changing. The code used in Synapse
proper should be compatible with both versions already.

This makes the CAS handler look more like the SAML/OIDC handlers:

* Render errors to users instead of throwing JSON errors.
* Internal reorganization.

Adds a new setting `email.invite_client_location` which, if defined, is
passed to the identity server during invites.

This adds an admin API that allows a server admin to get power in a room if a local user has power in a room. Will also invite the user if they're not in the room and its a private room. Can specify another user (rather than the admin user) to be granted power.

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

This had two effects 1) it'd give the wrong answer and b) would iterate
*all* power levels in the auth chain of each event. The latter of which
can be *very* expensive for certain types of IRC bridge rooms that have
large numbers of power level changes.

The final part (for now) of my work to implement a username picker in synapse itself. The idea is that we allow
`UsernameMappingProvider`s to return `localpart=None`, in which case, rather than redirecting the browser
back to the client, we redirect to a username-picker resource, which allows the user to enter a username.
We *then* complete the SSO flow (including doing the client permission checks).

The static resources for the username picker itself (in 
https://github.com/matrix-org/synapse/tree/rav/username_picker/synapse/res/username_picker)
are essentially lifted wholesale from
https://github.com/matrix-org/matrix-synapse-saml-mozilla/tree/master/matrix_synapse_saml_mozilla/res. 
As the comment says, we might want to think about making them customisable, but that can be a follow-up. 

Fixes #8876.

This fixes an KeyError exception, after this PR the content
is just considered unknown.

If we see stale extremities while persisting events, and notice that
they don't change the result of state resolution, we drop them.

... and disable coverage tracking for mypy and friends.