keycloak error : Unrecognized field “access_token”

I'm using keycloak to secure my rest API, I followed this tutorial to PROGRAMMATICALLY ADDING USERS, but I get that error message:

ERROR [io.undertow.request] (default task-9) UT005023: Exception handling request to /service/secured: org.jboss.resteasy.spi.UnhandledException: javax.ws.rs.client.ResponseProcessingException: javax.ws.rs.ProcessingException: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "access_token" (class org.keycloak.representations.AccessTokenResponse), not marked as ignorable (9 known properties: "notBeforePolicy", "otherClaims", "tokenType", "token", "expiresIn", "sessionState", "refreshExpiresIn", "idToken", "refreshToken"])
 at [Source: org.apache.http.conn.EofSensorInputStream@9d6aba2; line: 1, column: 18] (through reference chain: org.keycloak.representations.AccessTokenResponse["access_token"])
    at org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:76)
    at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:212)
    at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:149)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:372)
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:179)
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:220)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:86)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.keycloak.adapters.undertow.UndertowAuthenticatedActionsHandler.handleRequest(UndertowAuthenticatedActionsHandler.java:66)
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
    at io.undertow.server.handlers.DisableCacheHandler.handleRequest(DisableCacheHandler.java:33)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.security.handlers.AuthenticationConstraintHandler.handleRequest(AuthenticationConstraintHandler.java:51)
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
    at io.undertow.servlet.handlers.security.ServletSecurityConstraintHandler.handleRequest(ServletSecurityConstraintHandler.java:56)
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58)
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:72)
    at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
    at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.keycloak.adapters.undertow.ServletPreAuthActionsHandler.handleRequest(ServletPreAuthActionsHandler.java:69)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:282)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:261)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:80)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:172)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:199)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:774)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: javax.ws.rs.client.ResponseProcessingException: javax.ws.rs.ProcessingException: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "access_token" (class org.keycloak.representations.AccessTokenResponse), not marked as ignorable (9 known properties: "notBeforePolicy", "otherClaims", "tokenType", "token", "expiresIn", "sessionState", "refreshExpiresIn", "idToken", "refreshToken"])
 at [Source: org.apache.http.conn.EofSensorInputStream@9d6aba2; line: 1, column: 18] (through reference chain: org.keycloak.representations.AccessTokenResponse["access_token"])
    at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.extractResult(ClientInvocation.java:140)
    at org.jboss.resteasy.client.jaxrs.internal.proxy.extractors.BodyEntityExtractor.extractEntity(BodyEntityExtractor.java:58)
    at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientInvoker.invoke(ClientInvoker.java:104)
    at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientProxy.invoke(ClientProxy.java:62)
    at com.sun.proxy.$Proxy93.grantToken(Unknown Source)
    at org.keycloak.admin.client.token.TokenManager.grantToken(TokenManager.java:59)
    at org.keycloak.admin.client.token.TokenManager.getAccessToken(TokenManager.java:36)
    at org.keycloak.admin.client.token.TokenManager.getAccessTokenString(TokenManager.java:31)
    at org.keycloak.admin.client.resource.BearerAuthFilter.filter(BearerAuthFilter.java:31)
    at org.jboss.resteasy.client.jaxrs.internal.ClientInvocation.invoke(ClientInvocation.java:384)
    at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientInvoker.invoke(ClientInvoker.java:102)
    at org.jboss.resteasy.client.jaxrs.internal.proxy.ClientProxy.invoke(ClientProxy.java:62)
    at com.sun.proxy.$Proxy92.create(Unknown Source)
    at org.keycloak.quickstart.jaxrs.Resource.getSecured(Resource.java:47)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)

I searched in the net and found this solution but it doesn't work, I also find that discussion (I need more reputation to post the link :http:/lists.jboss.org/pipermail/keycloak-user/2014-November/001120.html) that explain the cause of the problem but I don't find a solution. can anyone help.

The Keycloak Admin Client (starting from version 1.9.0) supports the resteasy-jackson2-provider JSON provider out of the box, and this resolves the issue.

Use it in place of resteasy-jackson-provider in your pom.