The required mechanism 'SSO' is not available in mechanisms [FORM, BASIC] from the HttpAuthenticationFactory

Issue

• Application deployment fails when using custom Elytron realm and enable container managed single sign-on in Undertow:

ERROR [org.jboss.msc.service.fail] (ServerService Thread Pool -- 73) MSC000001: Failed to start service jboss.deployment.unit."servlet-security.war".undertow-deployment: org.jboss.msc.service.StartException in service jboss.deployment.unit."servlet-security.war".undertow-deployment: java.lang.RuntimeException: java.lang.IllegalStateException: The required mechanism 'SSO' is not available in mechanisms [FORM] from the HttpAuthenticationFactory.
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentService$1.run(UndertowDeploymentService.java:81)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
    ...
Caused by: java.lang.RuntimeException: java.lang.IllegalStateException: The required mechanism 'SSO' is not available in mechanisms [FORM] from the HttpAuthenticationFactory.
    at io.undertow.servlet.core.DeploymentManagerImpl.deploy(DeploymentManagerImpl.java:257)
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentService.startContext(UndertowDeploymentService.java:96)
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentService$1.run(UndertowDeploymentService.java:78)
    ... 8 more
Caused by: java.lang.IllegalStateException: The required mechanism 'SSO' is not available in mechanisms [FORM] from the HttpAuthenticationFactory.
    at org.wildfly.elytron.web.undertow.server.servlet.AuthenticationManager.initialSecurityHandler(AuthenticationManager.java:156)
    at org.wildfly.elytron.web.undertow.server.servlet.AuthenticationManager.lambda$configure$2(AuthenticationManager.java:101)
    at io.undertow.servlet.core.DeploymentManagerImpl.setupSecurityHandlers(DeploymentManagerImpl.java:445)
    at io.undertow.servlet.core.DeploymentManagerImpl.access$600(DeploymentManagerImpl.java:122)
    ...
ERROR [org.jboss.as.controller.management-operation] (Controller Boot Thread) WFLYCTL0013: Operation ("deploy") failed - address: ([("deployment" => "servlet-security.war")]) - failure description: {"WFLYCTL0080: Failed services" => {"jboss.deployment.unit.\"servlet-security.war\".undertow-deployment" => "java.lang.RuntimeException: java.lang.IllegalStateException: The required mechanism 'SSO' is not available in mechanisms [FORM] from the HttpAuthenticationFactory.
    Caused by: java.lang.RuntimeException: java.lang.IllegalStateException: The required mechanism 'SSO' is not available in mechanisms [FORM] from the HttpAuthenticationFactory.
    Caused by: java.lang.IllegalStateException: The required mechanism 'SSO' is not available in mechanisms [FORM] from the HttpAuthenticationFactory."}}
...

• Single Sign On Configuration is done as follows in the Undertow subsystem:

<subsystem xmlns="urn:jboss:domain:undertow:7.0" default-server="default-server" default-virtual-host="default-host" default-servlet-container="default" instance-id="${my.instance.id}" default-security-domain="my-security-domain">
                <buffer-cache name="default"/>
                <server name="default-server">
                    ...
                    <host name="default-host" alias="localhost">
                         ...
                         <single-sign-on/>
                    </host>