I want to utilise Google Meet api, which is used in Hangouts integration for Slack, description follows

TL;DR:

Links such as https://meet.google.com/new?gid=123&gd=qwe987 can be generated, so a modal is shown which can ask user's confirmation and then some request is sent from user's browser (where the Google Meet page is opened) to some endpoint (probably it is determined from gid which seems to be google application id). Is there a way to configure my application to have a webhook, so I can generate these custom links?

There's Google+ Hangouts app for Slack. Here's how it works (after you add the app in your workspace):

• you send /hangout command in any Slack channel
• slackbot sends an "Only visible to you" message in this channel with a link to start a new hangout. it looks smth like this (I changed data in the link): https://meet.google.com/new?gid=691521906844&gd=THTJ30X6W%7CU01113BD13M%7CD01113BDB5Z%7Csuren%7C%7C1846381238693%7C1%7CB01QFGG5GJF%7CE1MDm4DWcuVa0RbN5ZT9o5KF
• when you visit the link, a new meeting is started instantly, and the page shows modal with text "To bring others into this video call, post a link it to your Slack channel" with buttons 'Cancel' and 'Post'.
• when you click 'Post', a new message is sent to the Slack channel, where the command was sent. Text is "@Suren Khorenyan has started a Google+ Hangout and would like you to join. Join Hangout." and contains a link to the meet, which was created previously

How can I utilise this integration for another app, like Mattermost (or anything else like Telegram chats via bots)?

As I see, data in the url slightly changes. Probably it's payload for Google Meet to trigger Slack to send a message with link to the channel.

• gid seems to be something like google app id
• gd seems to be something like google data. If I url-decode it, it becomes THTJ30X6W|U01113BD13M|D01113BDB5Z|suren||1846381238693|1|B01QFGG5GJF|E1MDm4DWcuVa0RbN5ZT9o5KF. This is some kind of payload, separated by pipes (obviously), but I don't know what any part of this means (suren is my username in the Slack workspace, probably this is used for creating an invitation message).

When I click Post, this happens:

• a new POST request to https://hooks.slack.com/services/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 is sent with form-data

hangout_id: 1812381238693
hangout_url: https://meet.google.com//abc-iuqx-def

• a new message is posted to the Slack channel

Google meet somehow knows where to post back! Is this configured at the Google application (application id is provided via gid)? How can I configure my application for such behaviour? Where can I setup webhook url?

If we breakdown the request, we can see that url contains some parts of the gd payload:

• THTJ27X6W - this is the first part of the gd payload
• B01ABCD5GJF - last but one
• E1MDm4DWcuVa0RbK5ZT9o5KD - the last part of the gd payload

and form-data contains:

• hangout_id - this is in the gd payload after my name
• hangout_url - obviously, this is the url for the new created meeting

How can I change it for my needs?

I created a new application at Google APIs dashboard (here console.developers.google.com/apis), but can't find any docs for this integration. There's Google+ Hangouts API in API Library, but it says Apps will continue to function until April 25, 2017..

I tried to approach it from another side:

In the API Library there's Google Calendar. I found mattermost-hangout app on GitHub (had to update it a bit, so it works with updated api). Here's how it works:

• oauth2 for authorising at google (single account)
• it handles POST request, which is meant to be received from Mattermost (triggered by a slash command),
  • creates a new calendar event using Google Calendar API (with conference),
  • takes hangouts url from the response and sends a new message in the Mattermost channel with invitation to join the meeting.

But it has some downsides:

• you have to use one account to authorise all event creation events (yeah, it can be upgraded to authorise any number of users, but it'll be inconvenient. why to force anyone to provide access to their Google Account, when Google Meet authorisation just happens in browser, we don't need to create events)
• account, used for auth, now has events in his calendar. of course, events can be deleted, but it's not the way.

Is there any documentation on utilising gid and gd params?

Generally, I want to find a way to configure a webhook in my app, so when Google Meet finds my application's ID in the gid query param, it looks at the app's config and sends a request to my app (previously configured endpoint (I assume it works this way)).

Of course there's a chance that it's some kind of internal API and it cannot be used by everyone, but I could not find any information on this.