Maybe i can give you a qualitative answer withtout attitude.
What you want to do, is called local auth. Depending on the servermod you use, the syntax can deviate and you should check the auth.cfg in your sauerbraten server directory for more information on this. Note that some mods don't support this type of local auth and all the fuzzy things about global auth apply (see above).
Basically what you need to do are the following steps.
1. Open your sauerbraten client, type: "/genauthkeys" to generate a pair of keys.
2. get them somehow... (on windows you can copy if from the cmd log, in linux just from the shell and on mac... well, ask a mac user =) )
3. put the public key (starting with + or -) into your auth.cfg according to the syntax of the servermod.
in remod this would be: adduser [name] [public key]
4. make yourself a .cfg where you put in the private key (again according to the required syntax) and save this into your .cfg directory (don't ask me how to find this, as this makes me angry)
in remod this would be: authkey [name] [private key] remod
5. add "exec yourcfgname.cfg" into your autoexec.cfg
6. if all worked correctly you can now gain master by typing the magic words of your servermod
in remod : /auth remod
hope this helped you a lil bit more.
greetz
~ * ~