Two things I missed while implementing [MSC2140](https://github.com/matrix-org/matrix-doc/pull/2140/files#diff-c03a26de5ac40fb532de19cb7fc2aaf7R80).

1. Access tokens should be provided to the identity server as `access_token`, not `id_access_token`, even though the homeserver may accept the tokens as `id_access_token`.
2. Access tokens must be sent to the identity server in a query parameter, the JSON body is not allowed.

We now send the access token as part of an `Authorization: ...` header, which fixes both things.

The breaking code was added in https://github.com/matrix-org/synapse/pull/5892

Sytest PR: https://github.com/matrix-org/sytest/pull/697

Remove origin parameter from add_display_name_to_third_party_invite and add params to docstring (#6010)

Another small fixup noticed during work on a larger PR. The `origin` field of `add_display_name_to_third_party_invite` is not used and likely was just carried over from the `on_PUT` method of `FederationThirdPartyInviteExchangeServlet` which, like all other servlets, provides an `origin` argument.

Since it's not used anywhere in the handler function though, we should remove it from the function arguments.

Use account_threepid_delegate for 3pid validation

Only count real users when checking for auto-creation of auto-join room

Censor redactions in DB after a month

Signed-off-by: Jason Robinson <jasonr@matrix.org>

Add opentracing span for HTTP push

Signed-off-by: Jason Robinson <jasonr@matrix.org>

Signed-off-by: Jason Robinson <jasonr@matrix.org>

Signed-off-by: Jason Robinson <jasonr@matrix.org>

Previously if the first registered user was a "support" or "bot" user,
when the first real user registers, the auto-join rooms were not
created.

Fix to exclude non-real (ie users with a special user type) users
when counting how many users there are to determine whether we should
auto-create a room.

Signed-off-by: Jason Robinson <jasonr@matrix.org>

`sid` is required to be part of `three_pid_creds`. We were 500'ing if it wasn't provided instead of returning `M_MISSING_PARAM`.

Correctly handle non-bool m.federate flag

Move get_threepid_validation_session and delete_threepid_session into RegistrationWorkerStore

Fix destructuring assumption bug with using load_jinja2_templates

Co-Authored-By: Erik Johnston <erik@matrix.org>

Don't assume there is a 'self' arg in @trace decorator

Allow Synapse to send registration emails + choose Synapse or an external server to handle 3pid validation (#5987)

This is a combination of a few different PRs, finally all being merged into `develop`:

* #5875 
* #5876 
* #5868 (This one added the `/versions` flag but the flag itself was actually [backed out](https://github.com/matrix-org/synapse/commit/891afb57cbdf9867f2848341b29c75d6f35eef5a#diff-e591d42d30690ffb79f63bb726200891) in #5969. What's left is just giving /versions access to the config file, which could be useful in the future)
* #5835 
* #5969 
* #5940

Clients should not actually use the new registration functionality until https://github.com/matrix-org/synapse/pull/5972 is merged.

UPGRADE.rst, changelog entries and config file changes should all be reviewed closely before this PR is merged.