LDAP authentication

Guacamole supports LDAP authentication via an extension available from the main project website. This extension allows users and connections to be stored directly within an LDAP directory. If you have a centralized authentication system that uses LDAP, Guacamole’s LDAP support can be a good way to allow your users to use their existing usernames and passwords to log into Guacamole.

To use the LDAP authentication extension, you will need:

An LDAP directory as storage for all authentication data, such as OpenLDAP.
The ability to modify the schema of your LDAP directory.

The instructions here assume you already have an LDAP directory installed and working, and do not cover the initial setup of such a directory.

Important

This chapter involves modifying the contents of GUACAMOLE_HOME - the Guacamole configuration directory. If you are unsure where GUACAMOLE_HOME is located on your system, please consult Configuring Guacamole before proceeding.

How Guacamole uses LDAP

If the LDAP extension is installed, Guacamole will authenticate users against your LDAP server by attempting a bind as that user. The given username and password will be submitted to the LDAP server during the bind attempt.

If the bind attempt is successful, the set of available Guacamole connections is queried from the LDAP directory by executing an LDAP query as the bound user. Each Guacamole connection is represented within the directory as a special type of group: guacConfigGroup. Attributes associated with the group define the protocol and parameters of the connection, and users are allowed access to the connection only if they are associated with that group.

This architecture has a number of benefits:

Your users can use their existing usernames and passwords to log into Guacamole.
You can manage Guacamole connections using the same tool that you already use to manage your LDAP directory, such as Apache Directory Studio.
Existing security restrictions can limit visibility/accessibility of Guacamole connections.
Access to connections can easily be granted and revoked, as each connection is represented by a group.

Important

Though Guacamole connections can be stored within the LDAP directory, this is not required. Connection data can alternatively be stored within a database like MySQL or PostgreSQL as long as the LDAP username matches the username of the database user. Configuring Guacamole to use a database for authentication or connection storage is covered in Database authentication and later in this chapter in Associating LDAP with a database.

Downloading the LDAP extension

The LDAP authentication extension is available separately from the main guacamole.war. The link for this and all other officially-supported and compatible extensions for a particular version of Guacamole are provided on the release notes for that version. You can find the release notes for current versions of Guacamole here: http://guacamole.apache.org/releases/.

The LDAP authentication extension is packaged as a .tar.gz file containing:

guacamole-auth-ldap-1.5.1.jar: The Guacamole LDAP support extension itself, which must be placed in GUACAMOLE_HOME/extensions.
schema/: LDAP schema files. An .ldif file compatible with OpenLDAP is provided, as well as a .schema file compliant with RFC-2252. The .schema file can be transformed into the .ldif file automatically.

Preparing your LDAP directory (optional)

Although your LDAP directory already provides a means of storing and authenticating users, Guacamole also needs storage of connection configuration data, such as hostnames and ports, and a means of associating users with connections that they should have access to. You can do this either through modifying the LDAP directory schema, or through using a database like MySQL or PostgreSQL. If you do not wish to use the LDAP directory for connection storage, skip ahead to Associating LDAP with a database.

If you wish to store connection data directly within the LDAP directory, the required modifications to the LDAP schema are made through applying one of the provided schema files. These schema files define an additional object class, guacConfigGroup, which contains all configuration information for a particular connection, and can be associated with arbitrarily-many users and groups. Each connection defined by a guacConfigGroup will be accessible only by users who are members of that group (specified with the member attribute), or who are members of associated groups (specified with the seeAlso attribute).

Important

The instructions given for applying the Guacamole LDAP schema changes are specific to OpenLDAP, but other LDAP implementations, including Active Directory, will have their own methods for updating the schema.

If you are not using OpenLDAP, a standards-compliant schema file is provided that can be used to update the schema of any LDAP directory supporting RFC-2252. Please consult the documentation of your LDAP directory to determine how such schema changes can be applied.

The schema files are located within the schema/ directory of the archive containing the LDAP extension. You will only need one of these files:

guacConfigGroup.schema: A standards-compliant file describing the schema. This file can be used with any LDAP directory compliant with RFC-2252.
guacConfigGroup.ldif: An LDIF file compatible with OpenLDAP. This file was automatically built from the provided .schema file for convenience.

This chapter will cover applying guacConfigGroup.ldif to an OpenLDAP server. If you are not using OpenLDAP, your LDAP server should provide documentation for modifying its schema. If this is the case, please consult the documentation of your LDAP server before proceeding.

Applying the schema changes to OpenLDAP

Schema changes to OpenLDAP are applied using the ldapadd utility with the provided guacConfigGroup.ldif file:

# ldapadd -Q -Y EXTERNAL -H ldapi:/// -f schema/guacConfigGroup.ldif
adding new entry "cn=guacConfigGroup,cn=schema,cn=config"

#

If the guacConfigGroup object was added successfully, you should see output as above. You can confirm the presence of the new object class using ldapsearch:

# ldapsearch -Q -LLL -Y EXTERNAL -H ldapi:/// -b cn=schema,cn=config dn
dn: cn=schema,cn=config

dn: cn={0}core,cn=schema,cn=config

dn: cn={1}cosine,cn=schema,cn=config

dn: cn={2}nis,cn=schema,cn=config

dn: cn={3}inetorgperson,cn=schema,cn=config

dn: cn={4}guacConfigGroup,cn=schema,cn=config

#

Associating LDAP with a database

If you install both the LDAP authentication as well as support for a database (following the instructions in Database authentication), Guacamole will automatically attempt to authenticate against both systems whenever a user attempts to log in. In addition to any visible objects within the LDAP directory, that user will have access to any data associated with their account in the database, as well as any data associated with user groups that they belong to. LDAP user accounts and groups will be considered equivalent to database users and groups if their unique names are identical, as determined by the attributes given for the ldap-username-attribute and ldap-group-name-attribute properties.

Data can be manually associated with LDAP user accounts or groups by creating corresponding users or groups within the database which each have the same names. As long as the names are identical, a successful login attempt against LDAP will be trusted by the database authentication, and that user’s associated data will be visible.

If an administrator account (such as the default guacadmin user provided with the database authentication) has a corresponding user in the LDAP directory with permission to read other LDAP users and groups, the Guacamole administrative interface will include them in the lists presented to the administrator, and will allow connections from the database to be associated with those users or groups directly.

Installing LDAP authentication

Guacamole extensions are self-contained .jar files which are located within the GUACAMOLE_HOME/extensions directory. To install the LDAP authentication extension, you must:

Create the GUACAMOLE_HOME/extensions directory, if it does not already exist.
Copy guacamole-auth-ldap-1.5.1.jar within GUACAMOLE_HOME/extensions.
Configure Guacamole to use LDAP authentication, as described below.

Important

You will need to restart Guacamole by restarting your servlet container in order to complete the installation. Doing this will disconnect all active users, so be sure that it is safe to do so prior to attempting installation. If you do not configure the LDAP authentication properly, Guacamole will not start up again until the configuration is fixed.

Configuring Guacamole for LDAP

Additional properties may be added to guacamole.properties to describe how your LDAP directory is organized and how Guacamole should connect (and bind) to your LDAP server. Among these properties, only the ldap-user-base-dn property is required:

ldap-hostname

The hostname of your LDAP server. If omitted, “localhost” will be used by default. You will need to use a different value if your LDAP server is located elsewhere.

ldap-port

The port your LDAP server listens on. If omitted, the standard LDAP or LDAPS port will be used, depending on the encryption method specified with ldap-encryption-method (if any). Unencrypted LDAP uses the standard port of 389, while LDAPS uses port 636. Unless you manually configured your LDAP server to do otherwise, your LDAP server probably listens on port 389.

ldap-encryption-method

The encryption mechanism that Guacamole should use when communicating with your LDAP server. Legal values are “none” for unencrypted LDAP, “ssl” for LDAP over SSL/TLS (commonly known as LDAPS), or “starttls” for STARTTLS. If omitted, encryption will not be used.

If you do use encryption when connecting to your LDAP server, you will need to ensure that its certificate chain can be verified using the certificates in Java’s trust store, often referred to as cacerts. If this is not the case, you will need to use Java’s keytool utility to either add the necessary certificates or to create a new trust store containing those certificates.

If you will be using your own trust store and not the default cacerts, you will need to specify the full path to that trust store using the system property javax.net.ssl.trustStore. Note that this is a system property and not a Guacamole property; it must be specified when starting the JVM using the -D option. Your servlet container will provide some means of specifying startup options for the JVM.

ldap-max-search-results

The maximum number of search results that can be returned by a single LDAP query. LDAP queries which exceed this maximum will fail. This property is optional. If omitted, each LDAP query will be limited to a maximum of 1000 results.

ldap-search-bind-dn

The DN (Distinguished Name) of the user to bind as when authenticating users that are attempting to log in. If specified, Guacamole will query the LDAP directory to determine the DN of each user that logs in. If omitted, each user’s DN will be derived directly using the base DN specified with ldap-user-base-dn.

ldap-search-bind-password

The password to provide to the LDAP server when binding as ldap-search-bind-dn to authenticate other users. This property is only used if ldap-search-bind-dn is specified. If omitted, but ldap-search-bind-dn is specified, Guacamole will attempt to bind with the LDAP server without a password.

ldap-user-base-dn

The base of the DN for all Guacamole users. This property is absolutely required in all cases. All Guacamole users must be descendents of this base DN.

If a search DN is provided (via ldap-search-bind-dn), then Guacamole users need only be somewhere within the subtree of the specified user base DN.

If a search DN is not provided, then all Guacamole users must be direct descendents of this base DN, as the base DN will be appended to the username to derive the user’s DN. For example, if ldap-user-base-dn is “ou=people,dc=example,dc=net”, and ldap-username-attribute is “uid”, then a person attempting to login as “user” would be mapped to the following full DN: “uid=user,ou=people,dc=example,dc=net”.

ldap-username-attribute

The attribute or attributes which contain the username within all Guacamole user objects in the LDAP directory. Usually, and by default, this will simply be “uid”. If your LDAP directory contains users whose usernames are dictated by different attributes, multiple attributes can be specified here, separated by commas, but beware: doing so requires that a search DN be provided with ldap-search-bind-dn.

If a search DN is not provided, then the single username attribute specified here will be used together with the user base DN to directly derive the full DN of each user. For example, if ldap-user-base-dn is “ou=people,dc=example,dc=net”, and ldap-username-attribute is “uid”, then a person attempting to login as “user” would be mapped to the following full DN: “uid=user,ou=people,dc=example,dc=net”.

ldap-member-attribute

The attribute which contains the members within all group objects in the LDAP directory. Usually, and by default, this will simply be “member”. If your LDAP directory contains groups whose members are dictated by a different attribute, it can be specified here.

ldap-member-attribute-type

Specify whether the attribute defined in ldap-member-attribute (Usually “member”) identifies a group member by DN or by usercode. Possible values: “dn” (the default, if not specified) or “uid”.

Example: an LDAP server may present groups using the groupOfNames scheme:

dn: cn=group1,ou=Groups,dc=example,dc=net
objectClass: groupOfNames
cn: group1
gidNumber: 12345
member: user1,ou=People,dc=example,dc=net
member: user2,ou=People,dc=example,dc=net

ldap-member-attribute is member and ldap-member-attribute-type is dn.

Example: an LDAP server may present groups using the posixGroup scheme:

dn: cn=group1,ou=Groups,dc=example,dc=net
objectClass: posixGroup
cn: group1
gidNumber: 12345
memberUid: user1
memberUid: user2

ldap-member-attribute is memberUid and ldap-member-attribute-type is uid

ldap-user-attributes

The attribute or attributes to retrieve from the LDAP directory for the currently logged-in user, separated by commas. If specified, the attributes listed here are retrieved from each authenticated user and dynamically applied to the parameters of that user’s connections as parameter tokens with the prefix “LDAP_”.

When a user authenticates with LDAP and accesses a particular Guacamole connection, the values of these tokens will be the values of their corresponding attributes at the time of authentication. If the attribute has no value for the current user, then the corresponding token is not applied. If the attribute has multiple values, then the first value of the attribute is used.

When converting an LDAP attribute name into a parameter token name, the name of the attribute is transformed into uppercase with each word separated by underscores, a naming convention referred to as “uppercase with underscores” or “screaming snake case”.

For example:

LDAP Attribute	Parameter Token
`lowercase-with-dashes`	`${LDAP_LOWERCASE_WITH_DASHES}`
`CamelCase`	`${LDAP_CAMEL_CASE}`
`headlessCamelCase`	`${LDAP_HEADLESS_CAMEL_CASE}`
`lettersAndNumbers1234`	`${LDAP_LETTERS_AND_NUMBERS_1234}`
`aRANDOM_mixOf-3NAMINGConventions`	`${LDAP_A_RANDOM_MIX_OF_3_NAMING_CONVENTIONS}`

Usage of parameter tokens is discussed in more detail in Configuring Guacamole in Parameter tokens.

ldap-user-search-filter

The search filter used to query the LDAP tree for users that can log into and be granted privileges in Guacamole. If this property is omitted the default of (objectClass=*) will be used.

ldap-config-base-dn

The base of the DN for all Guacamole configurations. This property is optional. If omitted, the configurations of Guacamole connections will simply not be queried from the LDAP directory. If specified, this base DN will be used when querying the configurations accessible by a user once they have successfully logged in.

Each configuration is analogous to a connection. Within Guacamole’s LDAP support, each configuration functions as a group, having user members (via the member attribute) and optionally group members (via the seeAlso attribute), where each member of a particular configuration group will have access to the connection defined by that configuration.

ldap-group-base-dn

The base of the DN for all user groups that may be used by other extensions to define permissions or that may referenced within Guacamole configurations using the standard seeAlso attribute. All groups which will be used to control access to Guacamole configurations must be descendents of this base DN. If this property is omitted, the seeAlso attribute will have no effect on Guacamole configurations.

ldap-group-name-attribute

The attribute or attributes which define the unique name of user groups in the LDAP directory. Usually, and by default, this will simply be “cn”. If your LDAP directory contains groups whose names are dictated by different attributes, multiple attributes can be specified here, separated by commas.

ldap-group-search-filter

The search filter used to query the LDAP tree for groups that may be used by other extensions to define permissions. If this property is omitted the default of (objectClass=*) will be used.

ldap-dereference-aliases

Controls whether or not the LDAP connection follows (dereferences) aliases as it searches the tree. Possible values for this property are “never” (the default) so that aliases will never be followed, “searching” to dereference during search operations after the base object is located, “finding” to dereference in order to locate the search base, but not during the actual search, and “always” to always dereference aliases.

ldap-follow-referrals

This option controls whether or not the LDAP module follow referrals when processing search results from a LDAP search. Referrals can be pointers to other parts of an LDAP tree, or to a different server/connection altogether. This is a boolean parameter, with valid options of “true” or “false.” The default is false. When disabled, LDAP referrals will be ignored when encountered by the Guacamole LDAP client and the client will move on to the next result. When enabled, the LDAP client will follow the referral and process results within the referral, subject to the maximum hops parameter below.

ldap-max-referral-hops

This option controls the maximum number of referrals that will be processed before the LDAP client refuses to follow any more referrals. The default is 5. If the ldap-follow-referrals property is set to false (the default), this option has no effect. If the ldap-follow-referrals option is set to true, this will limit the depth of referrals followed to the number specified.

ldap-operation-timeout

This option sets the timeout, in seconds, of any single LDAP operation. The default is 30 seconds. When this timeout is reached LDAP operations will be aborted.

Again, even if the defaults are sufficient for the other properties, you must still specify the ldap-user-base-dn property. An absolutely minimal configuration for LDAP authentication will look like the following:

# LDAP properties
ldap-user-base-dn: ou=people,dc=example,dc=net

Using multiple LDAP servers

If you have several LDAP servers that Guacamole should authenticate against, it is possible to provide the configuration details for multiple servers by creating or editing a YAML file within GUACAMOLE_HOME called ldap-servers.yml. This file consists of a single list of servers (a YAML array of objects) and any number of corresponding configuration options (the key/value pairs within each YAML object). The available options correspond exactly to the properties described above except that they lack an ldap- prefix.

For example, the following guacamole.properties:

ldap-hostname: dc1.example.net
ldap-user-base-dn: ou=Users,dc=example,dc=net
ldap-username-attribute: sAMAccountName
ldap-search-bind-dn: cn=Guacamole,ou=Service Users,dc=example,dc=net
ldap-search-bind-password: SomePassword!

is exactly equivalent to the following ldap-servers.yml

- hostname: dc1.example.net
  user-base-dn: ou=Users,dc=example,dc=net
  username-attribute: sAMAccountName
  search-bind-dn: cn=Guacamole,ou=Service Users,dc=example,dc=net
  search-bind-password: SomePassword!

The benefit of using ldap-servers.yml is that the format allows multiple servers to be defined, relying on the properties within guacamole.properties as defaults. For example, the following ldap-servers.yml defines two LDAP servers:

- hostname: dc1.example.net
  user-base-dn: ou=Users,dc=example,dc=net
  username-attribute: sAMAccountName
  search-bind-dn: cn=Guacamole,ou=Service Users,dc=example,dc=net
  search-bind-password: SomePassword!

- hostname: dc2.example.net
  user-base-dn: ou=Users,dc=example,dc=net
  username-attribute: sAMAccountName
  search-bind-dn: cn=Guacamole,ou=Service Users,dc=example,dc=net
  search-bind-password: SomePassword!

Leveraging the fact that values within guacamole.properties are used as the default values for all LDAP servers in ldap-servers.yml, the above can be abbreviated by moving the common options into guacamole.properties:

ldap-user-base-dn: ou=Users,dc=example,dc=net
ldap-username-attribute: sAMAccountName
ldap-search-bind-dn: cn=Guacamole,ou=Service Users,dc=example,dc=net
ldap-search-bind-password: SomePassword!

Leaving ldap-servers.yml containing, simply:

- hostname: dc1.example.net
- hostname: dc2.example.net

If multiple LDAP servers are listed within ldap-servers.yml, and a user attempts to log into Guacamole, each defined LDAP server is tried, in order, until one server successfully authenticates the user or until all servers fail.

If not all LDAP servers are relevant to all users, and it is reasonable to determine which user is relevant to which LDAP server by the format of their username, patterns can be specified on a per-server basis to narrow which servers apply to which login attempts. For example:

- hostname: dc1.example.net
  match-usernames: COMPANYA\\(.*)

- hostname: dc2.example.net
  match-usernames: COMPANYB\\(.*)

The value for match-usernames can be any regular expression accepted by Java, where the capturing group dictates the portion that should be considered the user’s username with respect to Guacamole. If multiple patterns should apply to a particular LDAP server, this can be specified with a list of patterns for match-usernames:

- hostname: dc1.example.net
  match-usernames:
    - COMPANYA\\(.*)
    - (.*)@a\.example\.net

- hostname: dc2.example.net
  match-usernames:
    - COMPANYB\\(.*)
    - (.*)@b\.example\.net

Completing the installation

Guacamole will only reread guacamole.properties and load newly-installed extensions during startup, so your servlet container will need to be restarted before the LDAP authentication will take effect. Restart your servlet container and give the new authentication a try.

Important

You only need to restart your servlet container. You do not need to restart guacd.

guacd is completely independent of the web application and does not deal with guacamole.properties or the authentication system in any way. Since you are already restarting the servlet container, restarting guacd as well technically won’t hurt anything, but doing so is completely pointless.

If Guacamole does not come back online after restarting your servlet container, check the logs. Problems in the configuration of the LDAP extension will prevent Guacamole from starting up, and any such errors will be recorded in the logs of your servlet container. If properly configured, you will be able to log in as any user within the defined ldap-user-base-dn.

The LDAP schema

Guacamole’s LDAP support allows users and connections to be managed purely within an LDAP directory defined in guacamole.properties. This is accomplished with a minimum of changes to the standard LDAP schema - all Guacamole users are traditional LDAP users and share the same mechanism of authentication. The only new type of object required is a representation for Guacamole connections, guacConfigGroup, which was added to your server’s schema during the install process above.

Users

All Guacamole users, as far as the LDAP support is concerned, are LDAP users with standard LDAP credentials. When a user signs in to Guacamole, their username and password will be used to bind to the LDAP server. If this bind operation is successful, the available connections are queried from the directory and the user is allowed in.

Connections and parameters

Each connection is represented by an instance of the guacConfigGroup object class, an extended version of the standard LDAP groupOfNames, which provides a protocol and set of parameters. Only members of the guacConfigGroup will have access to the corresponding connection.

The guacConfigGroup object class provides two new attributes in addition to those provided by groupOfNames:

guacConfigProtocol

The protocol associated with the connection, such as “vnc” or “rdp”. This attribute is required for every guacConfigGroup and can be given only once.

guacConfigParameter

The name and value of a parameter for the specified protocol. This is given as name=value, where “name” is the name of the parameter, as defined by the documentation for the protocol specified, and “value” is any allowed value for that parameter.

This attribute can be given multiple times for the same connection.

For example, to create a new VNC connection which connects to “localhost” at port 5900, while granting access to user1 and user2, you could create an .ldif file like the following:

dn: cn=Example Connection,ou=groups,dc=example,dc=net
objectClass: guacConfigGroup
objectClass: groupOfNames
cn: Example Connection
guacConfigProtocol: vnc
guacConfigParameter: hostname=localhost
guacConfigParameter: port=5900
guacConfigParameter: password=secret
member: cn=user1,ou=people,dc=example,dc=net
member: cn=user2,ou=people,dc=example,dc=net

The new connection can then be created using the ldapadd utility:

$ ldapadd -x -D cn=admin,dc=example,dc=net -W -f example-connection.ldif
Enter LDAP Password:
adding new entry "cn=Example Connection,ou=groups,dc=example,dc=net"

$

Where cn=admin,dc=example,dc=net is an administrator account with permission to create new entries, and example-connection.ldif is the name of the .ldif file you just created.

There is, of course, no need to use only the standard LDAP utilities to create connections and users. There are useful graphical environments for manipulating LDAP directories, such as Apache Directory Studio, which make many of the tasks given above much easier.