When starting FitNesse you may specify a PasswordFile by using the -a command line argument. A PasswordFile consists of one username and password per line in the form of username:password.

Human Readable Passwords

This simple way to create a password file is to list each username:password pair as plain text in the PasswordFile. However this is not very secure in that anyone who is able to read the PasswordFile will have access to everyones password. Here's an example:
Leonardo:katana
Donatello:bo
Rafael:sai
Michaelangelo:nunchaku

4 users are defined here. Leonardo whose password is Katana, Donatello whose password is bo, Rafael whose password is sai, and Michaelangelo whose password is nunchaka.

Hashed Passwords

A password hashing program, similar to unix's passwd command, is provided with FitNesse. The Password program has the follwoing usage:
Usage: java fitnesse.authentication.Password [-f <password file>] [-c <password cipher>] <user>
        -f <password file> {passwords.txt}
        -c <password cipher> {fitnesse.authentication.HashingCipher} 

By using the Password program with default setting and using the same usernames and passwords as above, the file passwords.txt will be generated with the following content:
!fitnesse.authentication.HashingCipher
Leonardo:VEN4CfBvGCSafZDZNIKh
Donatello:VvkqQdgBBfCCZHzBUo6J
Michaelangelo:VBZ1TiB7HMptQsz3d3do
Rafael:YHVFNHr1fHaIGkLHMTSP

You can see that the passwords have been hashed and are not humanly readable. You may also notice a new line.
!fitnesse.authentication.HashingCipher
This should be left as is in the file. It tells the program with PasswordCipher to use when hashing the passwords. You may create your own PasswordCipher by implementing the fitnesse.authentication.PasswordCipher interface and use it for creating password files using the -c command line argument.