mongoose/docs/http/digest-auth.md

Digest Authentication

Mongoose has a built-in Digest (MD5) authentication support. In order to enable Digest authentication, create a file .htpasswd in the directory you would like to protect. That file should be in the format that Apache's htdigest utility.

You can use either Apache htdigest utility, or Mongoose pre-build binary at https://www.cesanta.com/binary.html to add new users into that file:

mongoose -A /path/to/.htdigest mydomain.com joe joes_password