红帽全球峰会7.2. One time password (OTP) authentication in Identity Management
One-time passwords bring an additional step to your authentication security. The authentication uses your password and an automatically generated one time password.
To generate one time passwords, you can use a hardware or software token. IdM supports both software and hardware tokens.
Identity Management supports the following standard OTP mechanisms:
- The HMAC-Based One-Time Password (HOTP) algorithm is based on a counter. HMAC stands for Hashed Message Authentication Code.
- The Time-Based One-Time Password (TOTP) algorithm is an extension of HOTP to support time-based moving factor.
IdM does not support OTP logins for Active Directory trust users.
The following security and other limitations currently relate to the OTP support in IdM:
- The most important security limitation is the potential vulnerability to replay attacks across the system. Replication is asynchronous, and an OTP code can therefore be reused during the replication period. A user might be able to log on to two servers at the same time. However, this vulnerability is usually difficult to exploit due to comprehensive encryption.
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It is not possible to obtain a ticket-granting ticket (TGT) using a client that does not support OTP authentication. This might affect certain use cases, such as authentication using the
mod_auth_kerbmodule or the Generic Security Services API (GSSAPI).
7.2.1. Available OTP authentication methods
When enabling OTP authentication, you can choose from the following authentication methods:
- Two-factor authentication (password + OTP)
- With this method, the user is always required to enter both a standard password and an OTP code.
- Password
- With this method, the user still has the option to authenticate using a standard password only.
- RADIUS proxy server authentication
- For information on configuring a RADIUS server for OTP validation in IdM, see Configuring a RADIUS server for OTP validation in IdM
- Global and user-specific authentication methods
You can configure these authentication methods either globally or for individual users:
- By default, user-specific authentication method settings take precedence over global settings. If no authentication method is set for a user, the globally-defined methods apply.
- You can disable per-user authentication method settings for any user. This ensures IdM ignores the per-user settings and always applies the global settings for the user.
- Combining multiple authentication methods
If you configure multiple authentication methods, any one of them will be sufficient to successfully authenticate the user. For example:
If you configure both two-factor and password authentication, the user must provide the password (first factor), but providing the OTP (second factor) is optional when using the command line:
First Factor: Second Factor (optional):- In the web UI, the user must still provide both factors.
However, a minor exception exists when RADIUS and another authentication method are configured:
- Kerberos always uses RADIUS, but LDAP does not. LDAP only recognizes the password and two-factor authentication methods.
- If you use an external two-factor authentication provider, use Kerberos from your applications. If you want to let users authenticate with a password only, use LDAP. It is recommended that the applications use Apache modules and SSSD, which allows configuring either Kerberos or LDAP.
7.2.2. GNOME Keyring service support
IdM integrates OTP authentication with the GNOME Keyring service. Note that GNOME Keyring integration requires the user to enter the first and second factors separately:
First factor: static_password
Second factor: one-time_password7.2.3. Offline authentication with OTP
IdM supports offline OTP authentication. However, to be able to log in offline, the user must first authenticate when the system is online by entering the static password and OTP separately:
First factor: static_password
Second factor: one-time_passwordIf the user enters both passwords separately like this when logging in online, the user can subsequently authenticate even if the central authentication server is unavailable. Note that IdM only prompts for the first-factor traditional static password when the user authenticates offline.
IdM also supports entering both the static password and OTP together in one string in the First factor prompt. However, this method is not compatible with offline OTP authentication. If the user enters both factors in a single prompt, IdM must contact the central authentication server to validate the credentials, which requires the system to be online.
If you use OTP authentication on devices that also operate offline, such as laptops, Red Hat recommends to enter the static password and OTP separately to make sure offline authentication is available. Otherwise, IdM does not allow you to log in after the system goes offline.
If you want to benefit from OTP offline authentication, apart from entering the static and OTP passwords separately, also make sure to meet the following conditions:
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The
cache_credentialsoption in the/etc/sssd/sssd.conffile is set toTrue, which enables caching the first factor password. -
The first-factor static password meets the password length requirement defined in the
cache_credentials_minimal_first_factor_lengthoption set in/etc/sssd/sssd.conf. The default minimal length is 8 characters. For more information about the option, see thesssd.conf(5)man page.
Even if the krb5_store_password_if_offline option is set to true in the /etc/sssd/sssd.conf file, SSSD does not attempt to refresh the Kerberos ticket-granting ticket (TGT) when the system returns to an online state. This is because the one-time password (OTP) may already be invalid at that point. To obtain a new TGT in this situation, the user must re-authenticate using both factors.
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