Chapter 16. guacamole-ext

While not strictly part of the Java API provided by the Guacamole project, guacamole-ext is an API exposed by the Guacamole web application within a separate project such that extensions, specifically authentication providers, can be written to tweak Guacamole to fit well in existing deployments.

Extensions to Guacamole can:

  1. Provide alternative authentication methods and sources of connection/user data.

  2. Theme or brand Guacamole through additional CSS files and static resources.

  3. Extend Guacamole's JavaScript code by providing JavaScript that will be loaded automatically.

  4. Add additional display languages, or alter the translation strings of existing languages.

Guacamole extension format

Guacamole extensions are standard Java .jar files which contain all classes and resources required by the extension, as well as the Guacamole extension manifest. There is no set structure to an extension except that the manifest must be in the root of the archive. Java classes and packages, if any, will be read from the .jar relative to the root, as well.

Beyond this, the semantics and locations associated with all other resources within the extension are determined by the extension manifest alone.

Extension manifest

The Guacamole extension manifest is a single JSON file, guac-manifest.json, which describes the location of each resource, the type of each resource, and the version of Guacamole that the extension was built for. The manifest can contain the following properties:


The version string of the Guacamole release that this extension is written for. This property is required for all extensions. The special version string "*" can be used if the extension does not depend on a particular version of Guacamole, but be careful - this will bypass version compatibility checks, and should never be used if the extension does more than basic theming or branding.


A human-readable name for the extension. This property is required for all extensions. When your extension is successfully loaded, a message acknowledging the successful loading of your extension by name will be logged.


A unique string which identifies your extension. This property is required for all extensions. This string should be unique enough that it is unlikely to collide with the namespace of any other extension.

If your extension contains static resources, those resources will be served at a path derived from the namespace provided here.


An array of the classnames of all AuthenticationProvider subclasses provided by this extension. Guacamole currently only supports one AuthenticationProvider being loaded at a time, thus this array must only contain one element, if it is present at all.


An array of all JavaScript files within the extension. All paths within this array must be relative paths, and will be interpreted relative to the root of the archive.

JavaScript files declared here will be automatically loaded when the web application loads within the user's browser.


An array of all CSS files within the extension. All paths within this array must be relative paths, and will be interpreted relative to the root of the archive.

CSS files declared here will be automatically applied when the web application loads within the user's browser.


An array of all translation files within the extension. All paths within this array must be relative paths, and will be interpreted relative to the root of the archive.

Translation files declared here will be automatically added to the available languages. If a translation file provides a language that already exists within Guacamole, its strings will override the strings of the existing translation.


An object where each property name is the name of a web resource file, and each value is the mimetype for that resource. All paths within this object must be relative paths, and will be interpreted relative to the root of the archive.

Web resources declared here will be made available to the application at app/ext/NAMESPACE/PATH, where NAMESPACE is the value of the namespace property, and PATH is the declared web resource filename.

The only absolutely required properties are guacamoleVersion, name, and namespace, as they are used to identify the extension and for compatibility checks. The most minimal guac-manifest.json will look something like this:

    "guacamoleVersion" : "0.9.7",
    "name" : "My Extension",
    "namespace" : "my-extension"

This will allow the extension to load, but does absolutely nothing otherwise. Lacking the semantic information provided by the other properties, no other files within the extension will be used. A typical guac-manifest.json for an extension providing theming or branding would be more involved:


    "guacamoleVersion" : "0.9.7",

    "name"      : "My Extension",
    "namespace" : "my-extension",

    "css" : [ "theme.css" ],

    "resources" : {
        "images/logo.png"   : "image/png",
        "images/cancel.png" : "image/png",
        "images/delete.png" : "image/png"


Accessing the server configuration

The configuration of the Guacamole server is exposed through the Environment interface, specifically the LocalEnvironment implementation of this interface. Through Environment, you can access all properties declared within, determine the proper hostname/port of guacd, and access the contents of GUACAMOLE_HOME.

Custom properties

If your extension requires generic, unstructured configuration parameters, is a reasonable and simple location for them. The Environment interface provides direct access to and simple mechanisms for reading and parsing the properties therein. The value of a property can be retrieved calling getProperty(), which will return null or a default value for undefined properties, or getRequiredProperty(), which will throw an exception for undefined properties.

For convenience, guacamole-ext contains several pre-defined property base classes for common types:

Class NameValue TypeInterpretation
BooleanGuacamolePropertyBooleanThe values "true" and "false" are parsed as their corresponding Boolean values. Any other value results in a parse error.
IntegerGuacamolePropertyIntegerNumeric strings are parsed as Integer values. Non-numeric strings will result in a parse error.
LongGuacamolePropertyLongNumeric strings are parsed as Long values. Non-numeric strings will result in a parse error.
StringGuacamolePropertyStringThe property value is returned as an untouched String. No parsing is performed, and parse errors cannot occur.
FileGuacamolePropertyFileThe property is interpreted as a filename, and a new File pointing to that filename is returned. If the filename is invalid, a parse error will be thrown. Note that the file need not exist or be accessible for the filename to be valid.

To use these types, you must extend the base class, implementing the getName() function to identify your property. Typically, you would declare these properties as static members of some class containing all properties relevant to your extension:

public class MyProperties {

    public static MY_PROPERTY = new IntegerGuacamoleProperty() {

        public String getName() { return "my-property"; }



Your property can then be retrieved with getProperty() or getRequiredProperty():

Integer value = environment.getProperty(MyProperties.MY_PROPERTY);

If you need more sophisticated parsing, you can also implement your own property types by implementing the GuacamoleProperty interface. The only functions to implement are getName(), which returns the name of the property, and parseValue(), which parses a given string and returns its value.

Advanced configuration

If you need more structured data than provided by simple properties, you can place completely arbitrary files in a hierarchy of your choosing anywhere within GUACAMOLE_HOME as long as you avoid placing your files in directories reserved for other purposes as described above.

The Environment interface exposes the location of GUACAMOLE_HOME through the getGuacamoleHome() function. This function returns a standard Java File which can then be used to locate other files or directories within GUACAMOLE_HOME:

File myConfigFile = new File(environment.getGuacamoleHome(), "my-config.xml");

There is no guarantee that GUACAMOLE_HOME or your file will exist, and you should verify this before proceeding further in your extension's configuration process, but once this is done you can simply parse your file as you see fit.

Authentication providers

The main use of guacamole-ext is to provide custom authentication for Guacamole through the implementation of authentication providers. An authentication provider is any class which implements the AuthenticationProvider interface, implementing the only function defined by that interface: getUserContext(). This function is required to return a "context" which provides access to only those users and configurations accessible with the given credentials, and enforces its own security model.

The credentials given are abstract and while Guacamole the web application implements a username/password driven login screen, you are not required to user usernames and passwords; the Credentials class given to the authentication provider provides access to all HTTP parameters in general, as well as cookies and SSL information.

The Guacamole web application includes a basic authentication provider implementation which parses an XML file to determine which users exist, their corresponding passwords, and what configurations those users have access to. This is the part of Guacamole that reads the user-mapping.xml file. If you use a custom authentication provider for your authentication, this file will probably not be required.

The community has implemented authentication providers which access databases, use LDAP, or even perform no authentication at all, redirecting all users to a single configuration specified in

A minimal authentication provider is implemented in the tutorials later, and the upstream authentication provider implemented within Guacamole, as well as the authentication providers implemented by the community, are good examples for how authentication can be extended without having to implement a whole new web application.


The SimpleAuthenticationProvider class provides a much simpler means of implementing authentication when you do not require the ability to add and remove users and connections. It is an abstract class and requires only one function implementation: getAuthorizedConfigurations().

This function is required to return a Map of unique IDs to configurations, where these configurations are all configurations accessible with the provided credentials. As before, the credentials given are abstract. You are not required to use usernames and passwords.

The configurations referred to by the function name are instances of GuacamoleConfiguration (part of guacamole-common), which is just a wrapper around a protocol name and set of parameter name/value pairs. The name of the protocol to use and a set of parameters is the minimum information required for other parts of the Guacamole API to complete the handshake required by the Guacamole protocol.

When a class that extends SimpleAuthenticationProvider is asked for more advanced operations by the web application, SimpleAuthenticationProvider simply returns that there is no permission to do so. This effectively disables all administrative functionality within the web interface.

If you choose to go the simple route, most of the rest of this chapter is irrelevant. Permissions, security model, and various classes will be discussed that are all handled for you automatically by SimpleAuthenticationProvider.

The UserContext

The UserContext is the root of all operations. It is used to list, create, modify, or delete users and connections, as well as to query available permissions.

The Guacamole web application uses permissions queries against the UserContext to determine what operations to present, but beware that it is up to the UserContext to actually enforce these restrictions. The Guacamole web application will not enforce restrictions on behalf of the UserContext.

The UserContext is the sole means of entry and the sole means of modification available to a logged-in user. If the UserContext refuses to perform an operation (by throwing an exception), the user cannot perform the operation at all.

Directory classes

Access to users and connections is given through Directory classes. These Directory classes are similar to Java collections, but they also embody object update semantics. Objects can be retrieved from a Directory using its get() function and added or removed with add() and remove() respectively, but objects already in the set can also be updated by passing an updated object to its update() function.

An implementation of a Directory can rely on these functions to define the semantics surrounding all operations. The add() function is called only when creating new objects, the update() function is called only when updating an object previously retrieved with get(), and remove() is called only when removing an existing object by its identifier.

When implementing an AuthenticationProvider, you must ensure that the UserContext will only return Directory classes that automatically enforce the permissions associated with all objects and the associated user.


The permissions system within guacamole-ext is an advisory system. It is the means by which an authentication module describes to the web application what a user is allowed to do. The body of permissions granted to a user describes which objects that user can see and what they can do to those objects, and thus suggests how the Guacamole interface should appear to that user.

Permissions are not the means by which access is restricted; they are purely a means of describing access level. An implementation may internally use the permission objects to define restrictions, but this is not required. It is up to the implementation to enforce its own restrictions by throwing exceptions when an operation is not allowed, and to correctly communicate the abilities of individual users through these permissions.

System permissions

System permissions describe access to operations that manipulate the system as a whole, rather than specific objects. This includes the creation of new objects, as object creation directly affects the system, and per-object controls cannot exist before the object is actually created.


The user is a super-user - the Guacamole equivalent of root. They are allowed to manipulate of system-level permissions and all other objects. This permission implies all others.


The user is allowed to create new connections. If a user has this permission, the management interface will display components related to connection creation, such as the "Manage" and "New Connection" buttons.


The user is allowed to create new connection groups. If a user has this permission, the management interface will display components related to connection group creation, such as the "Manage" and "New Group" buttons.


The user is allowed to create other users. If a user has this permission, the management interface will display components related to user creation, such as the "Manage" and "New User" buttons.

Object permissions

Object permissions describe access to operations that affect a particular object. Guacamole currently defines three types of objects which can be associated with permissions: users, connections, and connection groups. Each object permission associates a single user with an action that may be performed on a single object.


The user may grant or revoke permissions involving this object. "Involving", in this case, refers to either side of the permission association, and includes both the user to whom the permission is granted and the object the permission affects.


The user may delete this object. This is distinct from the ADMINISTER permission which deals only with permissions. A user with this permission will see the "Delete" button when applicable.


The user may see that this object exists and read the properties of that object.

Note that the implementation is not required to divulge the true underlying properties of any object. The parameters of a connection, the type or contents of a connection group, the password of a user, etc. all need not be exposed.

This is particularly important from the perspective of security when it comes to connections, as the parameters of a connection are only truly needed when a connection is being modified, and likely should not be exposed otherwise. The actual connection operation is always performed internally by the authentication provider, and thus does not require client-side knowledge of anything beyond the connection's existence.


The user may change the properties of this object.

In the case of users, this means the user's password can be altered. Permissions are not considered properties of a user, nor objects in their own right, but rather associations between a user and an action which may involve another object.

The properties of a connection include its name, protocol, parent connection group, and parameters. The properties of a connection group include its name, type, parent connection group, and children.

Connections and history

Authentication modules must return Connection objects which each implement a connect() function. When this function is called, the connection must be made if permission is available.

This new separation of concerns makes more sense when you consider that as connecting is an operation on a Connection, access to performing that operation must be restricted through the AuthenticationProvider, and thus must be enforced within the AuthenticationProvider. This separation also opens the door for things like load balancing of connections and restricting concurrent access to connections.

When a connection is made or terminated, it is also the duty of the authentication module to maintain the connection history. Each connection has a corresponding list of ConnectionRecord objects, each of which is associated with a past connection or a currently-active connection. This information will ultimately be exposed to the user as a history list when they view a connection in the management interface or as a simple active user count on the connection, advising the user of existing activity.