Cancel all Google/Firebase messaging subscriptions - google-cloud-messaging

Question

I just rewrote my firebase cloud messaging code for my web API and now use a Cloud Function to handle the subscriptions, or at least that is the theory.
Where can I go to cancel any existing subscriptions so that I can check that what seems now to be working, actually is (and that is not some hangover from before that is giving the impression of working).
This is all on a development instance of Firebase so I can delete whatever I want. I set up the subscriptions with the following code, which may or may not be coreect, but I think it means I need to look on Google rather than Firebase, but I can't find anything
let token = req.query.token;
let topic = "presents";
let uri = `https://iid.googleapis.com/iid/v1/${token}/rel/topics/${topic}`;
// Make the request to Google IID
var myHeaders = {
"Content-Type": "application/json",
Authorization: "key=" + secrets.devKey
};
var options = {
uri: uri,
method: "POST",
headers: myHeaders,
mode: "no-cors",
cache: "default"
};
rp(options)
.then(function(response) {
// console.log("rp success", response);
res.status(200).send({
msg: "Ok from Simon for " + token,
payload: response}
);
})
.catch(function(err) {
console.log("[fbm.registerForUpdates] Error registering for topic", err.message);
res.status(500).send(err);
});

Answer 1

The Firebase documentation seems to be incomplete on this topic. Playing around showed the following (valid at least at the time of writing, verified w/ Postman):
POST https://iid.googleapis.com/iid/v1/IID_TOKEN/rel/topics/TOPIC_NAME request creates a subscription for a topic & token
GET https://iid.googleapis.com/iid/info/IID_TOKEN?details=true request lists all subscribed topics for a token
DELETE https://iid.googleapis.com/iid/v1/IID_TOKEN/rel/topics/TOPIC_NAME request removes a subscription for a topic for a token
DELETE https://iid.googleapis.com/v1/web/iid/IID_TOKEN request removes all subscriptions for a token
On all these requests the header 'Authorization: key=YOUR_SERVER_KEY' needs to be set.
Sample output from a GET request:
{
"connectDate": "2018-10-06",
"application": "com.chrome.macosx",
"subtype": "wp:https://192.168.0.196:8020/#9885158F-953C-48BC-BCF5-38ABF2F89-V2",
"scope": "*",
"authorizedEntity": "30916174593",
"rel": {
"topics": {
"sensorUpdate": {
"addDate": "2018-10-07"
}
}
},
"connectionType": "WIFI",
"platform": "BROWSER"
}