Implement `/.well-known/matrix/client` endpoint

[infogulch]

I tried to log in via a new matrix client, Cinny, but login failed. Opening up the browser inspector I found that a GET request to https://my-cloudron-domain/.well-known/matrix/client was returning 404. /.well-known/matrix/client is a well known (pun intended) standard API endpoint used for server discovery. The matrix.org server serves at this endpoint:

{
    "m.homeserver": {
        "base_url": "https://matrix-client.matrix.org"
    },
    "m.identity_server": {
        "base_url": "https://vector.im"
    }
}

Cloudron already supports the /.well-known/matrix/server endpoint; I propose that support for the client endpoint is added as well.

[nebulon]

@infogulch have you seen and applied the settings mentioned at https://docs.cloudron.io/domains/#matrix-server-location ?

[infogulch]

@nebulon Yes, the matrix server location is already filled in. I've been using Synapse+Riot client on my server for several months and it's been working great. Specifically, the */server endpoint is currently working correctly and serves data as expected from https://my-cloudron-domain/.well-known/matrix/server :

{"m.server":"matrix.my-cloudron-domain.com:443"}

Note the difference between the existing endpoint and the new one:

https://my-cloudron-domain/.well-known/matrix/server < existing, works great
https://my-cloudron-domain/.well-known/matrix/client < what this thread is about

[nebulon]

@infogulch ah! thanks for the pointer, I was misreading this indeed. Looks like we have to add this then similarily like we have for matrix and mastodon.

[girish]

@infogulch This is easy to implement and I will add it in next release. But do you know why there are separate homeserver URL discovery endpoint for server and client ?

[infogulch]

Good question, I'm not sure. I guess */server is for federation (server<->server), and */client is for clients (client->server).

[girish]

I have fixed this for the next release.

$ curl -s https://example.com/.well-known/matrix/client | python3 -m json.tool
{
    "m.homeserver": {
        "base_url": "https://matrix.example.com"
    },
    "m.identity_server": {
        "base_url": "https://vector.im"
    }
}

[infogulch]

Hm, I'm not sure that the identity server is supposed to be pinned to vector.im... I'll see if someone on the matrix channel can chime in.

[infogulch]

@girish Ok I asked and @tulir on #matrix:matrix.org said that we can just omit the "m.identity_server" server field entirely. Apparently it's used to map third party ids (email/phone) to matrix ids. But since we're using cloudron logins we can just omit it.

Also note that that field is not marked as required on the API docs page.

[girish]

@infogulch ah thanks, i will remove it.