Keycloak spring security client credential grant

Question

I can use KeycloakRestTemplate where one keycloak client is communicating with another keycloak client. However it only works if I have logged into the first keycloak client, i.e. it sends client ID, client secret, username, password, to keycloak server. If I haven't authenticated with a user and password on the first client I get "Cannot set authorization header because there is no authenticated principle". But I have configured keycloak to use a service account for the first client (Client Credential Grant) therefore I should not be using a user/password and should be relying on client id/secret only. Is this is a bug/deviation from OAuth 2 spec?

Solution

KeycloakRestTemplate sends client ID, client secret, username and password to the Keycloak server. I wanted to only send client ID and secret. I created a KeycloakClientCredentialsRestTemplate subclass of OAuth2RestTemplate to do this. It uses OAuth2 support in Spring Boot to do a client credentials grant. It also takes Keycloak properties from application.properties.

import org.springframework.security.oauth2.client.OAuth2ClientContext;
import org.springframework.security.oauth2.client.OAuth2RestTemplate;
import org.springframework.security.oauth2.client.resource.OAuth2ProtectedResourceDetails;

public class KeycloakClientCredentialsRestTemplate extends OAuth2RestTemplate {

    public KeycloakClientCredentialsRestTemplate(OAuth2ProtectedResourceDetails resource,
            OAuth2ClientContext context) {
        super(resource, context);
    }

}

Also:

import java.util.ArrayList;
import java.util.List;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.security.oauth2.client.DefaultOAuth2ClientContext;
import org.springframework.security.oauth2.client.token.grant.client.ClientCredentialsResourceDetails;
import org.springframework.security.oauth2.common.AuthenticationScheme;
import org.springframework.stereotype.Service;

@Service
public class KeycloakClientCredentialsConfig {

    @Value("${keycloak.realm}")
    private String realm;

    @Value("${keycloak.auth-server-url}")
    private String authServerUrl;

    @Value("${keycloak.resource}")
    private String clientId;

    @Value("${keycloak.credentials.secret}")
    private String clientSecret;

    @Bean
    public KeycloakClientCredentialsRestTemplate createRestTemplate() {
        return new KeycloakClientCredentialsRestTemplate(getClientCredentialsResourceDetails(),
                new DefaultOAuth2ClientContext());
    }

    private ClientCredentialsResourceDetails getClientCredentialsResourceDetails() {
        String accessTokenUri = String.format("%s/realms/%s/protocol/openid-connect/token",
            authServerUrl, realm);
        List<String> scopes = new ArrayList<String>(0); // TODO introduce scopes

        ClientCredentialsResourceDetails clientCredentialsResourceDetails = 
                new ClientCredentialsResourceDetails();

        clientCredentialsResourceDetails.setAccessTokenUri(accessTokenUri);
        clientCredentialsResourceDetails.setAuthenticationScheme(AuthenticationScheme.header);
        clientCredentialsResourceDetails.setClientId(clientId);
        clientCredentialsResourceDetails.setClientSecret(clientSecret);
        clientCredentialsResourceDetails.setScope(scopes);

        return clientCredentialsResourceDetails;
    }

}