<chapter id="auth_spi">
    <title>Custom Authentication, Registration, and Required Actions</title>
    <para>
        Keycloak comes out of the box with a bunch of different authentication mechanisms: kerberos, password, and otp.
        These mechanisms may not meet all of your requirements and you may want to plug in your own custom ones.  Keycloak
        provides an authentication SPI that you can use to write new plugins.  The admin console supports applying, ordering,
        and configuring these new mechanisms.
    </para>
    <para>
        Keycloak also supports a simple registration form.  Different aspects of this form can be enabled and disabled i.e.
        Recaptcha support can be turned off and on.  The same authentication SPI can be used to add another page to the
        registration flow or reimplement it entirely.  There's also an additional fine-grain SPI you can use to add
        specific validations and user extensions to the built in registration form.
    </para>
    <para>
        A required action in Keycloak is an action that a user has to perform after he authenticates.  After the action
        is performed successfully, the user doesn't have to perform the action again.  Keycloak comes with some built in
        required actions like "reset password".  This action forces the user to change their password after they have logged in.
        You can write and plug in your own required actions.
    </para>
    <section>
        <title>Terms</title>
        <para>
            To first learn about the Authentication SPI, let's go over some of the terms used to describe it.
            <variablelist>
                <varlistentry>
                    <term>Authentication Flow</term>
                    <listitem>
                        <para>
                            A flow is a container for all authentications that must happen during login or registration.  If you
                            go to the admin console authentication page, you can view all the defined flows in the system and
                            what authenticators they are made up of.  Flows can contain other flows.  You can also bind a new
                            different flow for browser login, direct granta access, and registration.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Authenticator</term>
                    <listitem>
                        <para>
                            An authenticator is a pluggable component that hold the logic for performing the authentication
                            or action within a flow.  It is usually a singleton.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Execution</term>
                    <listitem>
                        <para>
                            An execution is an object that binds the authenticator to the flow and the authenticator
                            to the configuration of the authenticator.  Flows contain execution entries.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Execution Requirement</term>
                    <listitem>
                        <para>
                            Each execution defines how an authenticator behaves in a flow.  The requirement defines
                            whether the authenticator is enabled, disabled, optional, required, or an alternative.  An
                            alternative requirement means that the authentiactor is optional unless no other alternative
                            authenticator is successful in the flow.  For example, cookie authentication, kerberos,
                            and the set of all login forms are all alternative.  If one of those is successful, none of
                            the others are executed.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Authenticator Config</term>
                    <listitem>
                        <para>
                            This object defines the configuration for the Authenticator for a specific execution within
                            an authentication flow.  Each execution can have a different config.
                        </para>
                    </listitem>
                </varlistentry>
                <varlistentry>
                    <term>Required Action</term>
                    <listitem>
                        <para>
                            After authentication completes, the user might have one or more one-time actions he must
                            complete before he is allowed to login.  The user might be required to set up an OTP token
                            generator or reset an expired password or even accept a Terms and Conditions document.
                        </para>
                    </listitem>
                </varlistentry>
            </variablelist>
        </para>
    </section>
    <section>
        <title>Algorithm Overview</title>
        <para>
            Let's talk about how this all works for browser login. Let's assume the following flows, executions and sub flows.
<programlisting><![CDATA[
Cookie - ALTERNATIVE
Kerberos - ALTERNATIVE
Forms Subflow - ALTERNATIVE
           Username/Password Form - REQUIRED
           OTP Password Form - OPTIONAL
]]>
</programlisting>
        </para>
        <para>
            In the top level of the form we have 3 executions of which all are alternatively required.  This means that
            if any of these are successful, then the others do not have to execute.  The Username/Password form is not executed
            if there is an SSO Cookie set or a successful Kerberos login.  Let's walk through the steps from when a client
            first redirects to keycloak to authenticate the user.
            <orderedlist>
                <listitem>
                    <para>
                    The OpenID Connect or SAML protocol provider unpacks relevent data, verifies the client and any signatures.
                    It creates a ClientSessionModel.  It looks up what the browser flow should be, then starts executing the flow.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        The flow looks at the cookie execution and sees that it is an alternative.  It loads the cookie provider.
                        It checks to see if the cookie provider requires that a user already be associated with the client session.
                        Cookie provider does not require a user.   If it did, the flow would abort and the user would see an error screen.
                        Cookie provider then executes.  Its purpose is to see if there is an SSO cookie set.  If there is one set, it is validated
                        and the UserSessionModel is verified and associated with the ClientSessionModel.  The Cookie provider returns a
                        success() status if the SSO cookie exists and is validated.  Since the cookie provider returned success and each execution
                        at this level of the flow is ALTERNATIVE, no other execution is executed and this results in a successful login.
                        If there is no SSO cookie, the cookie provider returns with a status of attempted().  This means there was no error condition,
                        but no success either.  The provider tried, but the request just wasn't set up to handle this authenticator.
                    </para>
                </listitem>
                <listitem>
                    <para>
                    Next the flow looks at the Kerberos execution.  This is also an alternative.  The kerberos provider also does not
                    require a user to be already set up and associated with the ClientSessionModel so this provider is executed.
                    Kerberos uses the SPNEGO browser protocol.  This requires a series of challenge/responses between the server and client
                    exchanging negotiation headers.  The kerberos provider does not see any negotiate header, so it assumes that this is the
                    first interaction between the server and client.  It therefore creates an HTTP challenge response to the client and sets a
                    forceChallenge() status.  A forceChallenge() means that this HTTP response cannot be ignored by the flow and must be returned to the
                    client.  If instead the provider returned a challenge() status, the flow would hold the challenge response until all other alternatives
                    are attempted.  So, in this initial phase, the flow would stop and the challenge response would be sent back to the browser.  If the browser
                        then responds with a successful negotiate header, the provider associates the user with the ClientSession and the flow ends because
                        the rest of the executions on this level of the flow are all alternatives.  Otherwise, again, the kerberos provider
                        sets an attempted() status and the flow continues.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        The next execution is a subflow called Forms. The executions for this subflow are loaded and
                        the same processing logic occurs
                    </para>
                </listitem>
                <listitem>
                    <para>
                        The first execution in the Forms subflow is the UsernamePassword provider.  This provider also does not require for a user
                        to already be associated with the flow.  This provider creates challenge HTTP response and sets its status to challenge().
                        This execution is required, so the flow honors this challenge and sends the HTTP response back to the browser.  This
                        response is a rendering of the Username/Password HTML page.  The user enters in their username and password and clicks submit.
                        This HTTP request is directed to the UsernamePassword provider.  If the user entered an invalid username or password, a new
                        challenge response is created and a status of failureChallenge() is set for this execution.  A failureChallenge() means that
                        there is a challenge, but that the flow should log this as an error in the error log.  This error log can be used to lock accounts
                        or IP Addresses that have had too many login failures.  If the username and password is valid, the provider associated the
                        UserModel with the ClientSessionModel and returns a status of success()
                    </para>
                </listitem>
                <listitem>
                    <para>
                        The next execution is the OTP Form.  This provider requires that a user has been associated with the flow.  This requirement is satisfied
                        because the UsernamePassword provider already associated the user with the flow.  Since a user is required for this provider, the provider
                        is also asked if the user is configured to use this provider.  If user is not configured, and this execution is required, then the flow will
                        then set up a required action that the user must perform after authentication is complete.  For OTP, this means the OTP setup page.
                        If the execution was optional, then this execution is skipped.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        After the flow is complete, the authentication processor creates a UserSEssionModel and associates it with the ClientSEssionModel.
                        It then checks to see if the user is required to complete any required actions before logging in.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        First, each required action's evaluateTriggers() method is called.  This allows the required action provider to figure out if
                        there is some state that might trigger the action to be fired.  For example, if your realm has a password expiration policy,
                        it might be triggered by this method.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        Each required action associated with the user that has its requiredActionChallenge() method called.  Here the provider
                        sets up an HTTP response which renders the page for the required action.   This is done by setting a challenge status.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        If the required action is ultimately successful, then the required action is removed from the user's require actions list.
                    </para>
                </listitem>
                <listitem>
                    <para>
                        After all required actions have been resolved, the user is finally logged in.
                    </para>
                </listitem>
            </orderedlist>
        </para>
    </section>
    <section>
        <title>Authenticator SPI Walk Through</title>
        <para>
            In this section, we'll take a look at the Authenticator interface.  For this, we are going to implement an authenticator
            that requires that a user enter in the answer to a secret question like "What is your mother's maiden name?".  This example
            is fully implemented and contained in the examples/providers/authenticator directory of the demo distribution of Keycloak.
        </para>
        <para>
            The classes you must implement are the org.keycloak.authentication.AuthenticatorFactory and Authenticator interfaces.  The Authenticator
            interface defines the logic.  The AuthenticatorFactory is responsible for creating instances of an Authenticator.  They both extend
            a more generic Provider and ProviderFactory set of interfaces that other Keycloak components like User Federation do.
        </para>
        <section>
            <title>Packaging Classes and Deployment</title>
            <para>
                You will package your classes within a single jar.  This jar must contain a file named  <literal>org.keycloak.authentication.AuthenticatorFactory</literal>
                and must be contained in the <literal>META-INF/services/</literal> directory of your jar.  This file must list the fully qualified classname
                of each AuthenticatorFactory implementation you have in the jar.  For example:
        <programlisting>
            org.keycloak.examples.authenticator.SecretQuestionAuthenticatorFactory
            org.keycloak.examples.authenticator.AnotherProviderFactory
        </programlisting>
            </para>
            <para>
                This services/ file is used by Keycloak to scan the providers it has to load into the system.
            </para>
        </section>
        <section>
            <title>Implementing an Authenticator</title>
            <para>
                When implementing the Authenticator interface, the first method that needs to be implemented is the
                requiresUser() method.  For our example, this method must return true as we need to validate the secret question
                associated with the user.  A provider like kerberos would return false from this method as it can
                resolve a user from the negotiate header.  This example however is validating a specific credential of a specific
                user.
            </para>
            <para>
                The next method to implement is the configuredFor() method.  This method is responsible for determining if the
                user is configured for this particular authenticator.  For this example, we need to check of the answer to the
                secret question is been set up by the user or not.  In our case we are storing this information, hashed, within
                a UserCredentialValueModel within the UserModel (just like passwords are stored).  Here's how we do this
                very simple check:
<programlisting>
    @Override
    public boolean configuredFor(KeycloakSession session, RealmModel realm, UserModel user) {
        return session.users().configuredForCredentialType("secret_question", realm, user);
    }
</programlisting>
            </para>
            <para>
                The configuredForCredentialType() call queries the user to see if it supports that credential type.
            </para>
            <para>
                The next method to implement on the Authenticator is setRequiredActions().  If configuredFor() returns fales
                and our example authenticator is required within the flow, this method will be called.  It is response for
                registering any required actions that must be performed by the user.  In our example, we need to register
                a required action that will force the user to set up the answer to the secret question.  We will implement
                this required action provider later in this chapter.  Here is the implementation of the setRequiredActions()
                method.
<programlisting>
    @Override
    public void setRequiredActions(KeycloakSession session, RealmModel realm, UserModel user) {
        user.addRequiredAction("SECRET_QUESTION_CONFIG");
    }
</programlisting>
            </para>
            <para>
                Now we are getting into the meat of the Authenticator implementation.  The next method to implement is
                authenticate().  This is the initial method the flow invokes when the execution is first visited.
            </para>
        </section>
    </section>
</chapter>