This is for two reasons:
1. Suppresses duplicates correctly, as the notifier doesn't do any
duplicate suppression.
2. Makes it easier to connect the AppserviceHandler to the replication
stream.
It turns out that it's more useful to return a null device display name (and
let clients decide how to handle it: eg, falling back to device_id) than using
a constant string like "unknown device".
We should now be able to get our device_id from the access_token, so the
device_id on the upload request is optional. Where it is supplied, we should
check that it matches.
For active access_tokens without an associated device_id, we ought to register
the device in the devices table.
Also update the table on upgrade so that all of the existing e2e keys are
associated with real devices.
user_ips is kinda big, so really we want to add the index in the background
once we're running. Replace the schema delta with one which will do that.
I've done this in a way that's reasonably easy to reuse as there a few other
indexes I need, and I don't suppose they will be the last.
implement a GET /devices endpoint which lists all of the user's devices.
It also returns the last IP where we saw that device, so there is some dancing
to fish that out of the user_ips table.
Add a 'devices' table to the storage, as well as a 'device_id' column to
refresh_tokens.
Allow the client to pass a device_id, and initial_device_display_name, to
/login. If login is successful, then register the device in the devices table
if it wasn't known already. If no device_id was supplied, make one up.
Associate the device_id with the access token and refresh token, so that we can
get at it again later. Ensure that the device_id is copied from the refresh
token to the access_token when the token is refreshed.
