I don't understand what you mean about "web page should specify which IRC server to use". I'm also confused about notion about "request headers".
I highly doubt Convos will ever support chatting without JavaScript and CSS enabled.
I highly doubt Convos will ever support chatting without JavaScript and CSS enabled.
Too many web pages say IRC, and then if you select it just says "You must activate JavaScript to use IRC", without telling you what IRC server and channel to use, and that is no good.
However, I looked again and it also mentions an archive, which can be useful (for public channels) even if you are not using the web interface to connect to IRC. The archives should probably be available (perhaps configurable, in case you are using it privately and do not want public archives) even to those not using the web client.
The documentation mentions invite links and new user registration, so it does seem like it can be used for multiple users. Still, some users will want to use IRC directly (or might want to use IRC for communication but use the archives). Therefore, please fix it so that the IRC server to use (the value of window.__convos.default_connection, as far as the JavaScript code is concerned) is visible regardless of JavaScript/CSS enabled/disabled.
For archiving, I recommend supporting the "esologs" raw format, which works as follows: Each line begins with < or > indicating the direction of the message (where < means server to client and > means client to server), followed by a space, UNIX timestamp, space, microseconds, space, and then the full contents of the IRC command, uninterpreted. File names are like "YYYY-MM-DD-raw.txt" where "YYYY-MM-DD" is replaced by the date. For logs of an entire month, the format is "YYYY-MM-raw.txt". Replace "-raw.txt" with ".html" for formatted logs. (The esoteric programming IRC uses this format.)