Kerberos Authentication¶

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Overview
Kerberos Components and MongoDB
Operational Considerations
Kerberized MongoDB Environments
Testing and Verification

Overview¶

MongoDB Enterprise provides support for Kerberos authentication of MongoDB clients to mongod and mongos instances. Kerberos is an industry standard authentication protocol for large client/server systems. Kerberos allows MongoDB and applications to take advantage of existing authentication infrastructure and processes. MongoDB Enterprise only supports the MIT implementation of Kerberos.

Kerberos Components and MongoDB¶

Principals¶

In a Kerberos-based system, every participant in the authenticated communication is known as a “principal”, and every principal must have a unique name.

Principals belong to administrative units called realms. For each realm, the Kerberos Key Distribution Center (KDC) maintains a database of the realm’s principal and the principals’ associated “secret keys”.

For a client-server authentication, the client requests from the KDC a “ticket” for access to a specific asset. KDC uses the client’s secret and the server’s secret to construct the ticket which allows the client and server to mutually authenticate each other, while keeping the secrets hidden.

For the configuration of MongoDB for Kerberos support, two kinds of principal names are of interest: user principals and service principals.

User Principal¶

To authenticate using Kerberos, you must add the Kerberos user principals to MongoDB to the $external database. User principal names have the form:

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<username>@<KERBEROS REALM>

For every user you want to authenticate using Kerberos, you must create a corresponding user in MongoDB in the $external database.

Changed in version 3.6.3: To use sessions with $external authentication users (i.e. Kerberos, LDAP, x.509 users), the usernames cannot be greater than 10k bytes.

For examples of adding a user to MongoDB as well as authenticating as that user, see Configure MongoDB with Kerberos Authentication on Linux and Configure MongoDB with Kerberos Authentication on Windows.

Service Principal¶

Every MongoDB mongod and mongos instance (or mongod.exe or mongos.exe on Windows) must have an associated service principal. Service principal names have the form:

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<service>/<fully qualified domain name>@<KERBEROS REALM>

For MongoDB, the <service> defaults to mongodb. For example, if m1.example.com is a MongoDB server, and example.com maintains the EXAMPLE.COM Kerberos realm, then m1 should have the service principal name mongodb/m1.example.com@EXAMPLE.COM.

To specify a different value for <service>, use serviceName during the start up of mongod or mongos (or mongod.exe or mongos.exe). mongo shell or other clients may also specify a different service principal name using serviceName.

Service principal names must be reachable over the network using the fully qualified domain name (FQDN) part of its service principal name.

By default, Kerberos attempts to identify hosts using the /etc/krb5.conf file before using DNS to resolve hosts.

On Windows, if running MongoDB as a service, see Assign Service Principal Name to MongoDB Windows Service.

Linux Keytab Files¶

Linux systems can store Kerberos authentication keys for a service principal in keytab files. Each Kerberized mongod and mongos instance running on Linux must have access to a keytab file containing keys for its service principal.

To keep keytab files secure, use file permissions that restrict access to only the user that runs the mongod or mongos process.

Tickets¶

On Linux, MongoDB clients can use Kerberos’s kinit program to initialize a credential cache for authenticating the user principal to servers.

Windows Active Directory¶

Unlike on Linux systems, mongod and mongos instances running on Windows do not require access to keytab files. Instead, the mongod and mongos instances read their server credentials from a credential store specific to the operating system.

However, from the Windows Active Directory, you can export a keytab file for use on Linux systems. See Ktpass for more information.

Authenticate With Kerberos¶

To configure MongoDB for Kerberos support and authenticate, see Configure MongoDB with Kerberos Authentication on Linux and Configure MongoDB with Kerberos Authentication on Windows.

Operational Considerations¶

DNS¶

Each host that runs a mongod or mongos instance must have both A and PTR DNS records to provide forward and reverse lookup.

Without A and PTR DNS records, the host cannot resolve the components of the Kerberos domain or the Key Distribution Center (KDC).

System Time Synchronization¶

To successfully authenticate, the system time for each mongod and mongos instance must be within 5 minutes of the system time of the other hosts in the Kerberos infrastructure.

Kerberized MongoDB Environments¶

Driver Support¶

The following MongoDB drivers support Kerberos authentication:

Use with Additional MongoDB Authentication Mechanism¶

Although MongoDB supports the use of Kerberos authentication with other authentication mechanisms, only add the other mechanisms as necessary. See the Incorporate Additional Authentication Mechanisms section in Configure MongoDB with Kerberos Authentication on Linux and Configure MongoDB with Kerberos Authentication on Windows for details.

Testing and Verification¶

Introduced alongside MongoDB 4.4, the mongokerberos program provides a convenient method to verify your platform’s Kerberos configuration for use with MongoDB, and to test that Kerberos authentication from a MongoDB client works as expected. See the mongokerberos documentation for more information.

mongokerberos is available in MongoDB Enterprise only.

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