I've tried the proxy configuration and put upsource behind nginx https://www.jetbrains.com/upsource/help/2.0/proxy_configuration.html
However, it seems it's not supporting multiple server names. In nginx you can specify multiple domains separated by space:
server_name upsourceserver upsourceserver.mycompany.com
This way I can use a short name or the full domain name. However, when I use the name not specified by the upsource configure command I get an error message:
OAuth 2.0 Error
The client is not authorized to request an authorization entity using this method
I assume this use case is not supported yet. It would be nice to be able to use multiple domain names.