man htpasswd :

HTPASSWD(1)

NAME
htpasswd - Manage user files for basic authentication
SUMMARY
htpasswd is used to create and update the flat-files used to store usernames and password for basic authentication of HTTP users. If htpasswd can-
not access a file, such as not being able to write to the output file or not being able to read the file in order to update it, it returns an
error status and makes no changes.

Resources available from the Apache HTTP server can be restricted to just the users listed in the files created by htpasswd. This program can only
manage usernames and passwords stored in a flat-file. It can encrypt and display password information for use in other types of data stores,
though. To use a DBM database see dbmmanage.

htpasswd encrypts passwords using either a version of MD5 modified for Apache, or the system's crypt() routine. Files managed by htpasswd may con-
tain both types of passwords; some user records may have MD5-encrypted passwords while others in the same file may have passwords encrypted with
crypt().

This manual page only lists the command line arguments. For details of the directives necessary to configure user authentication in httpd see the
Apache manual, which is part of the Apache distribution or can be found at http://httpd.apache.org/.

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