To get your server working with Custom Login,
you can add a short invisible character sequence
to the end of your server's MOTD.
This will work even with vanilla servers.
Depending on your server software,
you might have to replace § with \u00A7.
The sequence consists of two colour codes, i.e. §[hex]§[hex]. The first one tells the client where to find the Yggdrasil metadata file, and the second one whether logging in is optional or mandatory. Here are the possible values for each, assuming your Minecraft server is at mc.example.com:
| Character | Location |
|---|---|
| 0 | http://mc.example.com/.well-known/yggdrasil.json |
| 1 | https://mc.example.com/.well-known/yggdrasil.json |
| 2 and 3 | As above, but replace mc.example.com with www.example.com |
| 4 and 5 | http(s)://ygg.example.com/meta.json |
| e | Ask user for location of the metadata file |
| f | Ask user for the actual API endpoints |
| Character | Meaning |
|---|---|
| 0 | Optional |
| 1 | Required |