I've read that it's possible to have multiple certificates on one domain. My question is whether all these certificates should be trusted and valid or whether one valid trusted certificate is enough for browsers to trust it.
The context is, I have a WebSocket chat server which provides a trusted certificate from Let's Encrypt through a proxy. However this server also provides an internally managed certificate for identifying it's part of a trusted network. This second certificate is meaningless towards browsers but required for connecting other chat servers to build up a network because the network all trust the root network ca and don't rely on domain names but identities instead.
So in essence, would browsers accept the server since the Let's Encrypt certificate is valid, even though the second certificate is untrusted (since the root ca is not part of the standard trust store).