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OpenDJ Attribute Uniqueness (and the Effects on OpenAM)

In real life we tend to value those traits that make us unique from others; but in an identity management deployment uniqueness is essential to the authentication process and should not be taken for granted.


Case in point, attributes in OpenDJ may share values that you may or may not want (or need) to be unique. For instance the following two (different) entries are both configured with the same value for the email address:

dn: uid=bnelson,ou=people,dc=example,dc=com
uid: bnelson
mail: bill.nelson@identityfusion.com
[LDIF Stuff Snipped]
dn: uid=scarter,ou=people,dc=example,dc=com
uid: scarter
mail: bill.nelson@identityfusion.com
[LDIF Stuff Snipped]

In some cases this may be fine, but in others this may not be the desired effect as you may need to enforce uniqueness for attributes such as uid, guid, email address, or simply credit cards. To ensure that attribute values are unique across directory server entries you need to configure attribute uniqueness.

UID Uniqueness Plug-In

OpenDJ has an existing plug-in that can be used to configure unique values for the uid attribute, but this plug-in is disabled by default.  You can find this entry in OpenDJ’s main configuration file (config.ldif) or by searching the cn=config tree in OpenDJ (assuming you have the correct permissions to do so).

dn: cn=UID Unique Attribute,cn=Plugins,cn=config
objectClass: ds-cfg-unique-attribute-plugin
objectClass: ds-cfg-plugin
objectClass: top
ds-cfg-enabled: false
ds-cfg-java-class: org.opends.server.plugins.UniqueAttributePlugin
ds-cfg-plugin-type: preOperationAdd
ds-cfg-plugin-type: preOperationModify
ds-cfg-plugin-type: preOperationModifyDN
ds-cfg-plugin-type: postOperationAdd
ds-cfg-plugin-type: postOperationModify
ds-cfg-plugin-type: postOperationModifyDN
ds-cfg-plugin-type: postSynchronizationAdd
ds-cfg-plugin-type: postSynchronizationModify
ds-cfg-plugin-type: postSynchronizationModifyDN
ds-cfg-invoke-for-internal-operations: true
ds-cfg-type: uid
cn: UID Unique Attribute

Leaving this plug-in disabled can cause problems with OpenAM, however, if OpenAM has been configured to authenticate using the uid attribute (and you ‘accidentally’ create entries with the same uid value). In such cases you will see an authentication error during the login process as OpenAM cannot determine which account you are trying to use for authentication.

Configuring Uniqueness

To fix this problem in OpenAM, you can use the OpenDJ dsconfig command to enable the UID Unique Attribute plug-in as follows:

./dsconfig set-plugin-prop --hostname localhost --port 4444  \
--bindDN "cn=Directory Manager" --bindPassword password \
--plugin-name "UID Unique Attribute" \
--set base-dn:ou=people,dc=example,dc=com --set enabled:true \
--trustAll --no-prompt

This will prevent entries from being added to OpenDJ where the value of any existing uids conflicts with the incoming entry’s uid.  This will address the situation where you are using the uid attribute for authentication in OpenAM, but what if you want to use a different attribute (such as mail) to authenticate? In such cases, you need to create your own uniqueness plug-in as follows:

./dsconfig create-plugin --hostname localhost --port 4444  \
--bindDN "cn=Directory Manager" --bindPassword password \
--plugin-name "Unique Email Address Plugin" \
--type unique-attribute --set type:mail --set enabled:true \
--set base-dn:ou=people,dc=example,dc=com --trustAll \

In both cases the base-dn parameter defines the scope where the the uniqueness applies. This is useful in multitenant environments where you may want to define uniqueness within a particular subtree but not necessarily across the entire server.


The uniqueness plug-in requires that you have an existing equality index configured for the attribute where you would like to enforce uniqueness.  The index is necessary so that OpenDJ can search for other entries (within the scope of the base-dn) where the attribute may already have a particular value set.

The following dscconfig command can be used to create an equality index for  the mail attribute:

./dsconfig  create-local-db-index  --hostname localhost --port 4444  \
--bindDN "cn=Directory Manager" --bindPassword password --backend-name userRoot  \
--index-name mail  --set index-type:equality --trustAll --no-prompt


OpenAM’s default settings (Data Store, LDAP authentication module, etc) uses the uid attribute to authenticate and uniquely identify a user.  OpenDJ typically uses uid as the unique naming attribute in a user’s distinguished name.  When combined together, it is almost assumed that you will be using the uid attribute in this manner, but that is not always the case.  You can easily run into issues when you start coloring outside of the lines and begin using other attributes (i.e. mail) for this purpose.  Armed with the information contained in this post, however, you should easily be able to configure OpenDJ to enforce uniqueness for any attribute.


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