I downloaded Keycloak version 2.5.1 example file. Extracted it onto a CentOS 7 machine, and installed Java-1.8.0 and java-devel. When I attempted to use the example file: /examples/providers/authenticator By typing: mvn clean install wildfly:deploy I got the following error on the terminal where I was executing mvn: ERROR] Failed to execute goal org.wildfly.plugins:wildfly-maven-plugin:1.1.0.Beta1:deploy (default-cli) on project authenticator-required-action-example: Failed to execute goal deploy: {"WFLYCTL0062: Composite operation failed and was rolled back. Steps that failed:" => {"Operation step-1" => {"WFLYCTL0080: Failed services" => {"jboss.deployment.unit.\"authenticator-required-action-example.jar\".POST_MODULE" => "org.jboss.msc.service.StartException in service jboss.deployment.unit.\"authenticator-required-action-example.jar\".POST_MODULE: WFLYSRV0153: Failed to process phase POST_MODULE of deployment \"authenticator-required-action-example.jar\" [ERROR] Caused by: java.lang.NoClassDefFoundError: Failed to link org/keycloak/examples/authenticator/SecretQuestionAuthenticatorFactory (Module \"deployment.authenticator-required-action-example.jar:main\" from Service Module Loader): org/keycloak/authentication/AuthenticatorFactory"}}}} [ERROR] -> [Help 1] [ERROR] [ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch. [ERROR] Re-run Maven using the -X switch to enable full debug logging. [ERROR] [ERROR] For more information about the errors and possible solutions, please read the following articles: [ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException [root@localhost authenticator]# pwd /root/keycloak-demo-2.5.1.Final/examples/providers/authenticator Thank you, Reed Lewis This was what was displayed on the Keycloak server. 12:06:20,685 INFO [org.jboss.as.server.deployment] (MSC service thread 1-1) WFLYSRV0027: Starting deployment of "authenticator-required-action-example.jar" (runtime-name: "authenticator-required-action-example.jar") 12:06:20,761 INFO [org.keycloak.subsystem.server.extension.KeycloakProviderDeploymentProcessor] (MSC service thread 1-4) Deploying Keycloak provider: {0} 12:06:20,767 WARN [org.jboss.modules] (MSC service thread 1-4) Failed to define class org.keycloak.examples.authenticator.SecretQuestionAuthenticatorFactory in Module "deployment.authenticator-required-action-example.jar:main" from Service Module Loader: java.lang.NoClassDefFoundError: Failed to link org/keycloak/examples/authenticator/SecretQuestionAuthenticatorFactory (Module "deployment.authenticator-required-action-example.jar:main" from Service Module Loader): org/keycloak/authentication/AuthenticatorFactory at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:446) at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:274) at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:78) at org.jboss.modules.Module.loadModuleClass(Module.java:605) at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:190) at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:363) at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:351) at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:93) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:348) at java.util.ServiceLoader$LazyIterator.nextService(ServiceLoader.java:370) at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:404) at java.util.ServiceLoader$1.next(ServiceLoader.java:480) at org.keycloak.provider.DefaultProviderLoader.load(DefaultProviderLoader.java:47) at org.keycloak.provider.ProviderManager.load(ProviderManager.java:93) at org.keycloak.services.DefaultKeycloakSessionFactory.loadFactories(DefaultKeycloakSessionFactory.java:206) at org.keycloak.services.DefaultKeycloakSessionFactory.deploy(DefaultKeycloakSessionFactory.java:112) at org.keycloak.provider.ProviderManagerRegistry.deploy(ProviderManagerRegistry.java:42) at org.keycloak.subsystem.server.extension.KeycloakProviderDeploymentProcessor.deploy(KeycloakProviderDeploymentProcessor.java:54) at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:147) at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1948) at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1881) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) 12:06:20,768 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-4) MSC000001: Failed to start service jboss.deployment.unit."authenticator-required-action-example.jar".POST_MODULE: org.jboss.msc.service.StartException in service jboss.deployment.unit."authenticator-required-action-example.jar".POST_MODULE: WFLYSRV0153: Failed to process phase POST_MODULE of deployment "authenticator-required-action-example.jar" at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:154) at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1948) at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1881) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: java.lang.NoClassDefFoundError: Failed to link org/keycloak/examples/authenticator/SecretQuestionAuthenticatorFactory (Module "deployment.authenticator-required-action-example.jar:main" from Service Module Loader): org/keycloak/authentication/AuthenticatorFactory at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.jboss.modules.ModuleClassLoader.defineClass(ModuleClassLoader.java:446) at org.jboss.modules.ModuleClassLoader.loadClassLocal(ModuleClassLoader.java:274) at org.jboss.modules.ModuleClassLoader$1.loadClassLocal(ModuleClassLoader.java:78) at org.jboss.modules.Module.loadModuleClass(Module.java:605) at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:190) at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:363) at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:351) at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:93) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:348) at java.util.ServiceLoader$LazyIterator.nextService(ServiceLoader.java:370) at java.util.ServiceLoader$LazyIterator.next(ServiceLoader.java:404) at java.util.ServiceLoader$1.next(ServiceLoader.java:480) at org.keycloak.provider.DefaultProviderLoader.load(DefaultProviderLoader.java:47) at org.keycloak.provider.ProviderManager.load(ProviderManager.java:93) at org.keycloak.services.DefaultKeycloakSessionFactory.loadFactories(DefaultKeycloakSessionFactory.java:206) at org.keycloak.services.DefaultKeycloakSessionFactory.deploy(DefaultKeycloakSessionFactory.java:112) at org.keycloak.provider.ProviderManagerRegistry.deploy(ProviderManagerRegistry.java:42) at org.keycloak.subsystem.server.extension.KeycloakProviderDeploymentProcessor.deploy(KeycloakProviderDeploymentProcessor.java:54) at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:147) ... 5 more 12:06:20,769 ERROR [org.jboss.as.controller.management-operation] (management-handler-thread - 4) WFLYCTL0013: Operation ("add") failed - address: ([("deployment" => "authenticator-required-action-example.jar")]) - failure description: {"WFLYCTL0080: Failed services" => {"jboss.deployment.unit.\"authenticator-required-action-example.jar\".POST_MODULE" => "org.jboss.msc.service.StartException in service jboss.deployment.unit.\"authenticator-required-action-example.jar\".POST_MODULE: WFLYSRV0153: Failed to process phase POST_MODULE of deployment \"authenticator-required-action-example.jar\" Caused by: java.lang.NoClassDefFoundError: Failed to link org/keycloak/examples/authenticator/SecretQuestionAuthenticatorFactory (Module \"deployment.authenticator-required-action-example.jar:main\" from Service Module Loader): org/keycloak/authentication/AuthenticatorFactory"}} 12:06:20,769 ERROR [org.jboss.as.server] (management-handler-thread - 4) WFLYSRV0021: Deploy of deployment "authenticator-required-action-example.jar" was rolled back with the following failure message: {"WFLYCTL0080: Failed services" => {"jboss.deployment.unit.\"authenticator-required-action-example.jar\".POST_MODULE" => "org.jboss.msc.service.StartException in service jboss.deployment.unit.\"authenticator-required-action-example.jar\".POST_MODULE: WFLYSRV0153: Failed to process phase POST_MODULE of deployment \"authenticator-required-action-example.jar\" Caused by: java.lang.NoClassDefFoundError: Failed to link org/keycloak/examples/authenticator/SecretQuestionAuthenticatorFactory (Module \"deployment.authenticator-required-action-example.jar:main\" from Service Module Loader): org/keycloak/authentication/AuthenticatorFactory"}} 12:06:20,772 INFO [org.jboss.as.server.deployment] (MSC service thread 1-1) WFLYSRV0028: Stopped deployment authenticator-required-action-example.jar (runtime-name: authenticator-required-action-example.jar) in 2ms 12:06:20,773 INFO [org.jboss.as.controller] (management-handler-thread - 4) WFLYCTL0183: Service status report WFLYCTL0186: Services which failed to start: service jboss.deployment.unit."authenticator-required-action-example.jar".POST_MODULE