Currently the UndertowXnioSsl, when acting like a client, uses the hostname of the URI to set the SNIHostName of the SSLParameters. For example here. This makes the SNI available when using a connection using hostname (https://localhost:8443/...) but impossible to set when using IP (https://127.0.0.1:8443/...).
This JIRA is to allow a new UndertowOption (for example SSL_SNI_HOSTNAME) that forces the SNI to the option value. That way using the IP but setting a SNIHostName would be possible. Something like the following: