Include context param in fxa_status webchannel message

[rfk]

When the browser wants to link out to FxA management pages on the web, it currently includes ?service=sync&context=fx_desktop_v3 query parameters, like so:

https://accounts.firefox.com/settings?service=sync&context=fx_desktop_v3

The presence of these query parameters causes accounts.firefox.com to send an fxa_status webchannel message to the browser to interrogate its login state, and the browser can choose whether to reply with the credentials of the signed-in user.

Now that it's possible to sign in to the browser without enabling sync, it doesn't really make sense to include service=sync in those links, and its presence there risks muddying FxA server-side metrics. We'd like to change these links to just be:

https://accounts.firefox.com/settings?context=fx_desktop_v3

For this to work, we'll need FxA to report the value of context in its fxa_status handshake message to the browser, so that the browser can decide whether or not to respond to the message without having to check for service=sync.

┆Issue is synchronized with this Jira Task
┆Issue Number: FXA-489

[vladikoff]

@rfk just to clarify you want the context both in the webchannel message AND in the query param?

[vladikoff]

from mtg: content --> browser, send the given context

[data-sync-user]

➤ Vladislav Filippov commented:

#4179 ( #4179 ) is the PR for this