vector.im identity server tries to contact homeserver on server_name instead of hostname

[AndreKR]

Description

Managing email addresses on the vector.im identity server fails when the server_name isn't the public_baseurl.

Steps to reproduce

On my Synapse homeserver I have set server_name to mydomain.tld and public_baseurl to https://matrix.mydomain.tld.

I have set up mydomain.tld/.well-known/matrix/server to respond with {"m.server": "matrix.mydomain.tld:443"} and mydomain.tld/.well-known/matrix/client to respond with {"m.homeserver": {"base_url": "https://matrix.mydomain.tld"}}.

Now I log into Element, go to All settings -> Security & Privacy. I see a spinner where the email addresses should be. In the console I see an error message:

M_UNKNOWN: MatrixError: [500] The Matrix homeserver returned invalid JSON (https://vector.im/_matrix/identity/v2/account/register)

When I check my webserver logs I see a request to https://mydomain.tld/_matrix/federation/v1/openid/userinfo?access_token=....

If I configure the webserver for mydomain.tld so that this request is forwarded to Synapse, then the Security & Privacy page starts working correctly.

However, I believe the identity server should not be contacting mydomain.tld at all, the request should go to https://matrix.mydomain.tld/_matrix/federation/v1/openid/userinfo?access_token=... instead.

Homeserver

Self-hosted Synapse

Synapse Version

1.144.0

Installation Method

Docker (matrixdotorg/synapse)

Database

SQLite

Workers

Single process

Platform

Docker on Ubuntu

Configuration

Just the generated YAML + email: config

Relevant log output

See above for the relevant error messages and URLs.

Anything else that would be useful to know?

No response