9. AccuRev Security Overview : User Authentication

User Authentication
With a few exceptions, a user cannot execute AccuRev commands unless he is authenticated as a registered AccuRev user. For authentication purposes, each registered AccuRev user has a username/password pair recorded in the database. A user’s password can be empty.
AccuRev automatically distinguishes two categories of users — those who have empty passwords, and those who have non-empty passwords. The keywords authuser and anyuser, respectively, are used by the ACL facility to designate these categories. See secinfo on page 222 of the AccuRev CLI User’s Guide for more information.
The “accurev_login” User-Authentication Method
AccuRev supports authenticating a user through an explicit login to the AccuRev Server. Using the GUI or the CLI, the user invokes the Login command and enters his password (possibly empty). This launches a user session, which is typically of limited duration (a few hours). When the session expires, the user must login again to continue using AccuRev.
The “custom” User-Authentication Method
AccuRev also supports script-based authentication of AccuRev users. This custom method works as follows:
The user invokes the login command through the AccuRev GUI or CLI client, and types a password.
The AccuRev Server invokes a script named server_auth_trig, passing it the username and password combination. The exit status of this script determines the success/failure of the Login command. See The ‘server_auth_trig’ Script for details.
This feature provides tremendous flexibility. For example, an authentication script could use an external user database, accessed through an LDAP interface, to perform AccuRev user authentication.
Authenticating a Replica User on the Master
Prior to V4.7.3, any authentication scheme on the master was only as trustworthy as the security of all the replica servers. The changes to replica authentication in AccuRev 4.7.3 allow sites using replication to deploy replicas to sites they may not trust to do user authentication, by allowing user authentication to be performed on the master server only.
Use the MASTER_AUTHENTICATES_LOGIN parameter in the acserver.cnf file on the master server:
If this parameter is set to true, user authentication is performed on the master server only. The master and replica servers must have the same authentication method. Only the accurev_login or custom authentication methods are allowed. The replica server must be able to contact the master server to log in; if the connection fails, the login fails.
To change the authentication method, change and restart the master server first, then change and restart all replicas.
If this parameter is set to false, user authentication can be performed on the replica, as before.
After changing the value of the parameter, restart the master server.
As a result of these changes, the XML input to the server_auth_trig script has changed to add server and port elements, which should contain the hostname and port of the master server.
The ‘server_auth_trig’ Script
The server_auth_trig user-authentication script, used by the custom user-authentication method, is similar to the server_admin_trig administrative trigger script. A sample script, implemented in Perl, is included in the AccuRev software distribution, in the examples subdirectory.
To deploy a user-authentication script, place an executable file in subdirectory triggers of the site_slice directory:
UNIX/Linux: the file must be named server_auth_trig or server_auth_trig.pl
Windows: the file must be named server_auth_trig.bat or server_auth_trig.exe
The script is called when a user invokes the AccuRev Login command. It executes in a subprocess of the AccuRev Server. The script’s standard input is a simple XML document, with the structure shown in this example:
(No password encryption is necessary, because this XML document is passed to the subprocess through an operating system pipe, not through a file.) The script’s standard output is appended to file triggers.log, located in the logs subdirectory of the site_slice directory. No output is required, however; only the script’s exit status is significant:
The user’s Login command also fails if the script does not execute properly — for example, if a runtime error occurs or the script file is not executable.
Selecting the User-Authentication Method
When you install AccuRev on the machine where the AccuRev Server process will run, the AccuRev Installation Wizard automatically sets the authentication method. Thereafter, you can switch methods with the authmethod command. Example:
accurev authmethod accurev_login
The switch takes place immediately. This might cause user confusion; it is not a command to run casually.
How AccuRev Records the User-Authentication Method
The current user-authentication method is stored in file preferences.xml in the site_slice directory. (Don’t confuse this with individual users’ preferences.xml files.) For example:
As an alternative to the authmethod command, you can change the user-authentication method by editing this file, then stopping and restarting the AccuRev Server process.
Restriction on Access to the “Add User” Command
User authentication is performed by the add-new-user command (GUI: Add User, CLI: mkuser). To prevent a chicken-and-egg problem, user authentication is bypassed if the AccuRev user registry is currently empty. After the first AccuRev user has been created, only an authenticated user can add users to the AccuRev user registry.

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