fun getAccessToken(singleScope: String): Deferred<AccessTokenInfo> (source)
Overrides FirefoxAccountShaped.getAccessToken
Tries to fetch an access token for the given scope.
scope - Single OAuth scope (no spaces) for which the client wants access
Unauthorized - We couldn't provide an access token for this scope.
The caller should then start the OAuth Flow again with the desired scope.
Return
AccessTokenInfo that stores the token, along with its scope, key and
expiration timestamp (in seconds) since epoch when complete