Enabling authentication and authorization involves complex functionality beyond a simple login API. In a previous article, I described the Keycloak REST login API endpoint, which only handles some authentication tasks. In this article, I describe how to enable other aspects of authentication and authorization by using Keycloak REST API functionality out of the box.

Authentication versus authorization

But first, what is the difference between authentication and authorization? Simply stated, authentication means who you are, while authorization means what can you do, with each approach using separate methods for validation. For example, authentication uses the user management and login form, and authorization uses role-based access control (RBAC) or an access control list (ACL).

Fortunately, these validation methods are provided in Red Hat's single sign-on (SSO) tools, or in their upstream open source project, Keycloak's REST API.

Keycloak SSO case study

To better understand using Keycloak for authentication and authorization, let's start with a simple case study. Suppose that Indonesia's Ministry of Education is planning to create a single sign-on integration with multiple schools. They plan to maintain their students' and teachers' single account IDs across multiple schools using a centralized platform. This lets each user have the same role, but with different access and privileges at each school, as shown in Figure 1.

The Ministry of Education containing the jakarta, bandung, and tangerang schools, with a teacher and student

Figure 1: Each user can use the same role, but with different access and privileges at each school.">

Keycloak SSO demo

Let's start the demo by creating a Keycloak realm. Using the Add realm dialog box for this ministry (as shown in Figure 2). Name the realm education, set Enabled to ON, and click Create.

The add realm dialog filled out with the settings in the text.

Figure 2: Create a Keycloak realm for the Ministry of Education named "education."

Next, go to the Roles page and make sure the Realm Roles tab is selected, as shown in Figure 3.

Create a Keycloak realm for the Ministry of Education named "education."
Figure 3: Create two separate roles for the education realm: teacher and student.

Click Add Role to create two separate roles for this realm called "teacher" and "student." These new roles will then appear in the Realm Roles tab as shown in Figure 4.

Roles -> Realm Roles showing the newly added roles

Figure 4: Add the teacher and student roles.

Then, using the Clients page, click Create to add a client, as shown in Figure 5.

The Clients page with the Create button highlighted
Figure 5: Add a client.

On the Add Client page, create a client named jakarta-school, and click Save to add this client, as shown in Figure 6.

Clients -> Add Client with Client ID jakarta-school and client protocol openid-connect

On the jakarta-school details page, go to the Settings tab and enter the following client configuration, as shown in Figure 7:

  • Client ID: jakarta-school
  • Enabled: ON
  • Consent Required: OFF
  • Client Protocol: openid-connect
  • Access Type: confidential
  • Standard Flow Enabled: ON
  • Impact Flow Enabled: OFF
  • Direct Access Grants Enabled: ON
Clients -> jakarta-school with the Settings filled out
Figure 7: On the jakarta-school details page, enter the client configuration.

At the bottom of the same page, on the Authentication Flow Overrides part, we can set to the following as shown in Figure 8:

  • Browser Flow: browser
  • Direct Grant Flow: direct grant
Authentication Flow Overrides filled in

Figure 8: Configure the authentication flow overrides.

Go to the Roles tab, click Add Role, and create the create-student-grade, view-student-grade, and view-student-profile roles for this client as shown in Figure 9. Each should be set to Composite False.

Clients -> jakarta-school with 3 roles showing in the Roles tab
Figure 9: Create roles for this client.

Next, go to the Client Scopes tab and in the Default Client Scopes section, add "roles" and "profile" to the Assigned Default Client Scopes, as shown in Figure 10.

jakarta-school -> Client Scopes tab -> Setup with default client scopes assigned
Figure 10: Set the client scopes.

On the jakarta-school details page, select Mappers and then Create Protocol Mappers, and set mappers to display the client roles on the Userinfo API, as shown in Figure 11:

  • Name: roles
  • Mapper Type: User Realm Role
  • Multivalued: ON
  • Token Claim Name: roles
  • Claim JSON Type: String
  • Add to ID token: OFF
  • Add to access token: OFF
  • Add to userinfo: ON
Clients -> jakarta-school ->Mappers -> Create Protocol Mappers filled out for the example
Figure 11: Set the mappers to display the client roles.

Next, go to the Users page, select Add user, create the new users, and click Save as shown in Figure 12:

  • Username: edwin
  • Email:
  • First Name: Edwin
  • Last Name: M
  • User Enabled: ON
  • Email Verified: OFF
Users -> Add user with the information filled in
Figure 12: Create the new users.

And finally, in the Role Mappings tab, select the Client Roles for each user in jakarta-school, as shown in Figure 13. These should be create-student-grade, view-student-grade, and view-student-profile.

Users -> edwin -> Role Mappings with the Client Roles selected
Figure 13: Select the Client Roles for each user in jakarta-school.

This concludes my demo of the Keycloak configuration.

Keycloak connection using a Java application

Now I want to demonstrate how to develop a very simple Java application. This application connects to your Keycloak instances and uses Keycloak's authentication and authorization capability through its REST API.

First, develop the Java application starting with a pom.xml file, as shown in the following sample:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns=""










The Java application also requires you to develop a simple properties file:

server.port = 8082

keycloak.scope=openid, profile



Next, get the Keycloak certificate ID from the form shown in Figure 14.

Education -&gt; Keys -&gt; Active with the RSA-generated key selected.
Figure 14:
Figure 14: Find the Keycloak certificate ID.

After that, and most importantly, your next task is to develop the integration code; several Keycloak APIs are involved in this action. Note that I did not go into detail about the Keycloak login API as it is already described in my previous article.

Start with a simple logout API:

        private String keycloakLogout;
    public void logout(String refreshToken) throws Exception {
        MultiValueMap<String, String> map = new LinkedMultiValueMap<>();

        HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, null);
        restTemplate.postForObject(keycloakLogout, request, String.class);

First, I want to point out that, for logging out, it's critical that you use your refresh_token parameter and not access_token. Now, use the API to check for whether a bearer token is valid and active or not, in order to validate whether a request is bringing a valid credential.

    private String keycloakUserInfo;
    private String getUserInfo(String token) {
        MultiValueMap<String, String> headers = new LinkedMultiValueMap<>();
        headers.add("Authorization", token);

        HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(null, headers);
        return restTemplate.postForObject(keycloakUserInfo, request, String.class);

For authorization, you can use two approaches to decide whether a given role is eligible to access a specific API. The first approach is to determine what role a bearer token brings by verifying it against Keycloak's userinfo API, and the next approach is to validate a role within the bearer token.

For the first approach, you can expect the following response from Keycloak:

    "sub": "ef2cbe43-9748-40e5-aed9-fe981e3082d5",
    "roles": [
    "name": "Edwin M",
    "preferred_username": "edwin",
    "given_name": "Edwin",
    "family_name": "M"

As you can see, there is a roles tag there and one approach is to validate the access right based on that. The drawback is the multiple roundtrip request between your application and Keycloak for each request, which results in higher latency.

Another approach is to read the contents of the JWT token, which are sent through each request. In order to successfully decode your JWT token, you must know what public key is used for signing it. That's why Keycloak provides a JWKS endpoint. You can view its content by using the curl command, as shown in the following sample:

$ curl -L -X GET 'http://localhost:8080/auth/realms/education/protocol/openid-connect/certs'

For this previous sample, the result is as follows:

    "keys": [
            "kid": "vdaec4Br3ZnRFtZN-pimK9v1eGd3gL2MHu8rQ6M5SiE",
            "kty": "RSA",
            "alg": "RS256",
            "use": "sig",
            "n": "4OPCc_LDhU6ADQj7cEgRei4VUf4PZH8GYsxsR6RSdeKmDvZ48hCSEFiEgfc3FIfh-gC4r9PtKucc_nkRofrAKR4qL8KNNoSuzQAOC92Yz6r7Ao4HppHJ8-QVdo5H-d9wfNSlDLBSo5My4b4EnHb1HLuFxDqyhFpGvsoUJdgbt3m_Q3WAVb2yrM83S6HX__vrQvqUk2e7z5RNrI7LSsW3ZOz9fU7pvm8-kFFAIPJ7fOJIC7UQ9wBWg3YdwQ0B2b24jXjVr0QCGzqJ6o1G_UZYSJCDMGQDpDcEuYnvSKBLfVR-0EcAjolRhcSPjHlW0Cp0YU8qwWDHpjkbrMrFmxlO4Q",
            "e": "AQAB"

Note that, in the previous sample, kid means key id, alg is the algorithm, and n is the public key used for this realm. You can use this public key to easily decode our JWT token, and read roles from the JWT claim. The sample decoded JWT token is shown next:

  "jti": "85edca8c-a4a6-4a4c-b8c0-356043e7ba7d",
  "exp": 1598079154,
  "nbf": 0,
  "iat": 1598078854,
  "iss": "http://localhost:8080/auth/realms/education",
  "sub": "ef2cbe43-9748-40e5-aed9-fe981e3082d5",
  "typ": "Bearer",
  "azp": "jakarta-school",
  "auth_time": 0,
  "session_state": "f8ab78f8-15ee-403d-8db7-7052a8647c65",
  "acr": "1",
  "realm_access": {
    "roles": [
  "resource_access": {
    "jakarta-school": {
      "roles": [
  "scope": "profile",
  "name": "Edwin M",
  "preferred_username": "edwin",
  "given_name": "Edwin",
  "family_name": "M"

You can read the roles tag by using the code shown in the following sample:

    public HashMap teacher(@RequestHeader("Authorization") String authHeader) {
        try {
            DecodedJWT jwt = JWT.decode(authHeader.replace("Bearer", "").trim());

            // check JWT is valid
            Jwk jwk = jwtService.getJwk();
            Algorithm algorithm = Algorithm.RSA256((RSAPublicKey) jwk.getPublicKey(), null);


            // check JWT role is correct
            List<String> roles = ((List)jwt.getClaim("realm_access").asMap().get("roles"));
                throw new Exception("not a teacher role");

            // check JWT is still active
            Date expiryDate = jwt.getExpiresAt();
            if(expiryDate.before(new Date()))
                throw new Exception("token is expired");

            // all validation passed
            return new HashMap() {{
                put("role", "teacher");
        } catch (Exception e) {
            logger.error("exception : {} ", e.getMessage());
            return new HashMap() {{
                put("status", "forbidden");

The best part of this approach is that you can place the public key from Keycloak in a cache, which reduces the round-trip request, and this practice eventually increases application latency and performance. The full code for this article can be found in my GitHub repository.


In conclusion, I prepared this article first to explain that enabling authentication and authorization involves complex functionality, beyond just a simple login API. Then I demonstrated how to enable many aspects of authentication and authorization using Keycloak REST API functionality out of the box.

In addition, I demonstrated how to develop a simple Java application that connects to your Keycloak instances, and uses Keycloak's authentication and authorization capability through its REST API.

Last updated: February 27, 2024