Registration: Allow registration without a username

[matrixbot]

This issue was originally created by @anoadragon453 at matrix-org/dendrite#400.

Spec URL: https://matrix.org/docs/spec/client_server/r0.3.0.html#post-matrix-client-r0-register

If omitted, the homeserver MUST generate a Matrix ID local part.

Phase: 1

We currently do not generate a username if username is not set as part of a POST request to /register.

Sent Request

{
    "password": "asd",
    "auth": {
        "type": "m.login.dummy",
        "session": "Mxa1dMHgfP2VTIFNNgSkDL5n"
    }
}

Received Response

Synapse:

{
  "access_token": "...",
  "home_server": "amorgan.xyz",
  "user_id": "@15:amorgan.xyz",
  "device_id": "IGKRGSXVFW"
}

Dendrite:

{
  "errcode": "M_INVALID_USERNAME",
  "error": "User ID can only contain characters a-z, 0-9, or '_-./'"
}

I believe Synapse will just set the new username to the next available user ID. So for instance, if my homeserver has registered 3 users, the newly generated username would be @4:homeserver.xyz. We can either use this method or some other method that generates ID in an increasing manner.

Summary:

• Don't error out if a username is not provided as part of registration
• Generate and return a new username if one was not provided
• Create test case(s) that checks for a successful registration without a username, and that the returned generated username is valid

[matrixbot]

This comment was originally posted by @jsinghrai at matrix-org/dendrite#400 (comment).

Mind If I take this issue.

[matrixbot]

This comment was originally posted by @anoadragon453 at matrix-org/dendrite#400 (comment).

@jsinghrai Go for it!

[matrixbot]

This comment was originally posted by @anoadragon453 at matrix-org/dendrite#400 (comment).

We currently validate usernames here:

https://github.com/matrix-org/dendrite/blob/dfcf31f293a319830e2b8a188413db776930a5e5/src/github.com/matrix-org/dendrite/clientapi/routing/register.go#L373-L378

If there is no username, then we should generate one instead and use that.