Single Sign-On with Keycloak

This guide explains how to enable single sign-on (SSO) for applications being proxied by F5 NGINX Plus. The solution uses OpenID Connect as the authentication mechanism, with Keycloak as the Identity Provider (IdP), and NGINX Plus as the Relying Party, or OIDC client application that verifies user identity.

This guide applies to NGINX Plus Release 36 and later. In earlier versions, NGINX Plus relied on an njs-based solution, which required NGINX JavaScript files, key-value stores, and advanced OpenID Connect logic. Starting from NGINX Plus version R34, the new OpenID Connect module simplifies this process to just a few directives.

Prerequisites

• An NGINX Plus subscription and NGINX Plus Release 36 or later. For installation instructions, see Installing NGINX Plus.

• A domain name pointing to your NGINX Plus instance, for example, demo.example.com.

Configure Keycloak

1. Log in to your Keycloak admin console, for example, https://<keycloak-server>/admin/master/console/.

2. In the left navigation, go to Clients, then

3. Select Create client and provide the following details:

   • Set Client type to OpenID Connect.

   • Enter a Client ID, for example, nginx-demo-app. You will need it later when configuring NGINX Plus.

   • Select Next.

4. In the Capability Config section:

   • Set Client Authentication to On. This sets the client type to confidential.

   • Select Next.

5. In the Login Settings section:

   Add a Redirect URI, for example:

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   https://demo.example.com/oidc_callback

   Add a Post Logout Redirect URI to support RP-initiated logout, for example:

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   https://demo.example.com/post_logout/

   • Select Save.

6. In the Credentials tab, make note of the Client Secret. You will need it later when configuring NGINX Plus.

Configure Logout and Front-Channel Single Logout (optional)

Front-channel logout allows Keycloak to notify NGINX Plus when a user signs out of the realm or another application that participates in Single Logout (SLO). Keycloak sends a front-channel HTTP request (typically loaded in a hidden iframe) to a logout URL that you configure for the client.

1. In the Keycloak admin console, go to Clients and select your nginx-demo-app client.

2. On the Settings tab, scroll to the Logout settings section.

3. Configure front-channel logout for this client:

   • Set Front channel logout to On.

   • In Front-channel Logout URL, enter the NGINX Plus front-channel logout endpoint, for example:

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     https://demo.example.com/front_logout

   • Enable Front-channel logout session required. With this option enabled, Keycloak includes both the session identifier (sid) and issuer (iss) parameters in the front-channel logout request that it sends to NGINX Plus, as defined by the OpenID Connect Front-Channel Logout specification. NGINX Plus uses these parameters to identify and clear the corresponding user session.

Assign Users or Groups

This step is optional, and is necessary if you need to restrict or organize user permissions.

1. In the Roles tab, add a Client Role, for example, nginx-keycloak-role.

2. Under Users, create a new user or select a user.

3. In Role Mappings, assign a role to the user within the nginx-demo-app client.

Get the OpenID Connect Discovery URL

Check the OpenID Connect Discovery URL. By default, Keycloak publishes the .well-known/openid-configuration document at the following address:

https://<keycloak-server>/realms/<realm_name>/.well-known/openid-configuration.

1. Run the following curl command in a terminal:

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   curl https://<keycloak-server>/realms/<realm_name>/.well-known/openid-configuration | jq

   Where:

   • the <keycloak-server> is your Keycloak server address

   • the <realm_name> is your Keycloak realm name

   • the /.well-known/openid-configuration is the default address for Keycloak for document location

   • the jq command (optional) is used to format the JSON output for easier reading and requires the jq JSON processor to be installed.

   The configuration metadata is returned in the JSON format:

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   {
       ...
       "issuer": "https://<keycloak-server>/realms/<realm_name>",
       "authorization_endpoint": "https://<keycloak-server>/realms/<realm_name>/protocol/openid-connect/auth",
       "token_endpoint": "https://<keycloak-server>/realms/<realm_name>/protocol/openid-connect/token",
       "jwks_uri": "https://<keycloak-server>/realms/<realm_name>/protocol/openid-connect/certs",
       "userinfo_endpoint": "https://<keycloak-server>/realms/<realm_name>/protocol/openid-connect/userinfo",
       "end_session_endpoint": "https://<keycloak-server>/realms/<realm_name>/protocol/openid-connect/logout",
       ...
   }

2. Copy the issuer value, you will need it later when configuring NGINX Plus. Typically, the OpenID Connect Issuer for Keycloak is https://<keycloak-server>/realms/<realm_name>.

You will need the values of Client ID, Client Secret, and Issuer in the next steps.

Set up NGINX Plus

With Keycloak configured, you can enable OIDC on NGINX Plus. NGINX Plus serves as the Relying Party (RP) application — a client service that verifies user identity.

1. Ensure that you are using the latest version of NGINX Plus by running the nginx -v command in a terminal:

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   nginx -v

   The output should match NGINX Plus Release 36 or later:

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   nginx version: nginx/1.29.3 (nginx-plus-r36)

2. Ensure that you have the values of the Client ID, Client Secret, and Issuer obtained during Keycloak Configuration.

3. In your preferred text editor, open the NGINX configuration file (/etc/nginx/nginx.conf for Linux or /usr/local/etc/nginx/nginx.conf for FreeBSD).

4. In the http {} context, make sure your public DNS resolver is specified with the resolver directive: By default, NGINX Plus re‑resolves DNS records at the frequency specified by time‑to‑live (TTL) in the record, but you can override the TTL value with the valid parameter:

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   http {
       resolver 10.0.0.1 ipv4=on valid=300s;
   
       # ...
   }

5. In the http {} context, define the Keycloak provider named keycloak by specifying the oidc_provider {} context:

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   http {
       resolver 10.0.0.1 ipv4=on valid=300s;
   
       oidc_provider keycloak {
   
           # ...
   
       }
       # ...
   }

6. In the oidc_provider {} context, specify:

   • your actual Keycloak Client ID obtained in Keycloak Configuration with the client_id directive

   • (if not using PKCE) your Client Secret obtained in Keycloak Configuration with the client_secret directive

   • the Issuer URL obtained in Keycloak Configuration with the issuer directive

     The issuer is typically your Keycloak OIDC URL:

     https://<keycloak-server>/realms/<realm_name>.

     By default, NGINX Plus creates the metadata URL by appending the /.well-known/openid-configuration part to the Issuer URL. If your metadata URL is different, you can explicitly specify it with the config_url directive.

   • The logout_uri is URI that a user visits to start an RP‑initiated logout flow.

   • The post_logout_uri is absolute HTTPS URL where Keycloak should redirect the user after a successful logout. This value must also be configured in the Keycloak client’s Post Logout Redirect URIs.

   • If the logout_token_hint directive set to on, NGINX Plus sends the user’s ID token as a hint to Keycloak. This directive is optional, however, if it is omitted the Keycloak may display an extra confirmation page asking the user to approve the logout request.

   • The frontchannel_logout_uri directive defines the URI on NGINX Plus that receives OpenID Connect front-channel logout requests from Keycloak. This path must be an HTTPS endpoint and must match the Front-channel Logout URL configured for the client in Keycloak. When a front-channel logout request is sent (typically in a hidden iframe), Keycloak includes the session identifier and issuer (the sid and iss parameters, when Front-channel logout session required is enabled); the OIDC module uses these values to locate and clear the corresponding local session.

   • If the userinfo directive is set to on, NGINX Plus will fetch /protocol/openid-connect/userinfo from the Keycloak and append the claims from userinfo to the $oidc_claims_ variables.

   • PKCE (Proof Key for Code Exchange) is automatically enabled when Keycloak’s OpenID Connect discovery document advertises the S256 code challenge method in the code_challenge_methods_supported field. You can override this behavior with the pkce directive: set pkce off; to disable PKCE even when S256 is advertised, or pkce on; to force PKCE even if the IdP metadata does not list S256.

   • The module automatically selects the client authentication method for the token endpoint based on the provider metadata token_endpoint_auth_methods_supported. When only client_secret_post is advertised, NGINX Plus uses the client_secret_post method and sends the client credentials in the POST body. When both client_secret_basic and client_secret_post are present, the module prefers HTTP Basic (client_secret_basic), which remains the default for Keycloak.

   • Important

     All interaction with the IdP is secured exclusively over SSL/TLS, so NGINX must trust the certificate presented by the IdP. By default, this trust is validated against your system’s CA bundle (the default CA store for your Linux or FreeBSD distribution). If the IdP’s certificate is not included in the system CA bundle, you can explicitly specify a trusted certificate or chain with the ssl_trusted_certificate directive so that NGINX can validate and trust the IdP’s certificate.

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   http {
       resolver 10.0.0.1 ipv4=on valid=300s;
   
       oidc_provider keycloak {
           issuer            https://<keycloak-server>/realms/<realm_name>;
           client_id         <client_id>;
           client_secret     <client_secret>;
           logout_uri        /logout;
           post_logout_uri   https://demo.example.com/post_logout/;
           logout_token_hint on;
           frontchannel_logout_uri /front_logout;
           userinfo          on;
   
           # Optional: PKCE configuration. By default, PKCE is automatically
           # enabled when the IdP advertises the S256 code challenge method.
           # pkce on;
       }
   
       # ...
   }

7. Make sure you have configured a server that corresponds to demo.example.com, and there is a location that points to your application (see Step 10) at http://127.0.0.1:8080 that is going to be OIDC-protected:

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   http {
       # ...
   
       server {
           listen      443 ssl;
           server_name demo.example.com;
   
           ssl_certificate     /etc/ssl/certs/fullchain.pem;
           ssl_certificate_key /etc/ssl/private/key.pem;
   
           location / {
   
               # ...
   
               proxy_pass http://127.0.0.1:8080;
           }
       }
       # ...
   }

8. Protect this location with Keycloak OIDC by specifying the auth_oidc directive that will point to the keycloak configuration specified in the oidc_provider {} context in Step 5:

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   # ...
   location / {
        auth_oidc keycloak;
   
        # ...
   
        proxy_pass http://127.0.0.1:8080;
   }
   # ...

9. Pass the OIDC claims as headers to the application (Step 10) with the proxy_set_header directive. These claims are extracted from the ID token returned by Keycloak:

   • $oidc_claim_sub - a unique Subject identifier assigned for each user by Keycloak

   • $oidc_claim_email the e-mail address of the user

   • $oidc_claim_name - the full name of the user

   • any other OIDC claim using the $oidc_claim_ variable

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   # ...
   location / {
        auth_oidc keycloak;
   
        proxy_set_header sub   $oidc_claim_sub;
        proxy_set_header email $oidc_claim_email;
        proxy_set_header name  $oidc_claim_name;
   
        proxy_pass http://127.0.0.1:8080;
   }
   # ...

10. Provide endpoint for completing logout:

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    # ...
    location /post_logout/ {
         return 200 "You have been logged out.\n";
         default_type text/plain;
    }
    # ...

11. Create a simple test application referenced by the proxy_pass directive which returns the authenticated user’s full name and email upon successful authentication:

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    # ...
    server {
        listen 8080;
    
        location / {
            return 200 "Hello, $http_name!\nEmail: $http_email\nKeycloak sub: $http_sub\n";
            default_type text/plain;
        }
    }

12. Save the NGINX configuration file and reload the configuration:

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    nginx -s reload

Complete Example

This configuration example summarizes the steps outlined above. It includes only essential settings such as specifying the DNS resolver, defining the OIDC provider, configuring SSL, and proxying requests to an internal server.

http {
    # Use a public DNS resolver for Issuer discovery, etc.
    resolver 10.0.0.1 ipv4=on valid=300s;

    oidc_provider keycloak {
        # The 'issuer' typically matches your Keycloak realm's base URL:
        # For example: https://<keycloak-server>/realms/<realm_name>
        issuer https://<keycloak-server>/realms/master;

        # Replace with your actual Keycloak client_id and secret
        client_id <client_id>;
        client_secret <client_secret>;

        # RP‑initiated logout
        logout_uri /logout;
        post_logout_uri https://demo.example.com/post_logout/;
        logout_token_hint on;

        # Front-channel logout (OP‑initiated single sign-out)
        frontchannel_logout_uri /front_logout;

        # Fetch userinfo claims
        userinfo on;

        # Optional: PKCE configuration
        # pkce on;

        # If the .well-known endpoint can't be derived automatically,
        # specify config_url:
        # config_url https://<keycloak-server>/realms/master/.well-known/openid-configuration;
    }

    server {
        listen 443 ssl;
        server_name demo.example.com;

        ssl_certificate /etc/ssl/certs/fullchain.pem;
        ssl_certificate_key /etc/ssl/private/key.pem;

        location / {
            # Protect this location with Keycloak OIDC
            auth_oidc keycloak;

            # Forward OIDC claims as headers if desired
            proxy_set_header sub $oidc_claim_sub;
            proxy_set_header email $oidc_claim_email;
            proxy_set_header name $oidc_claim_name;

            proxy_pass http://127.0.0.1:8080;
        }

        location /post_logout/ {
            return 200 "You have been logged out.\n";
            default_type text/plain;
        }
    }

    server {
        # Simple test upstream server
        listen 8080;

        location / {
            return 200 "Hello, $http_name!\nEmail: $http_email\nKeycloak sub: $http_sub\n";
            default_type text/plain;
        }
    }
}

Testing

1. Open https://demo.example.com/ in a browser. You should be redirected to Keycloak’s login page for your realm.

2. Enter valid Keycloak credentials for a user assigned to the nginx-demo-app client. Upon successful sign-in, Keycloak redirects you back to NGINX Plus, and you will see the proxied application content (for example, "Hello, Jane Doe!").

3. Navigate to https://demo.example.com/logout. NGINX Plus initiates an RP‑initiated logout; Keycloak ends the session and redirects back to https://demo.example.com/post_logout/.

4. Refresh https://demo.example.com/ again. You should be redirected to Keycloak for a fresh sign‑in, proving the session has been terminated.

Legacy njs-based Keycloak Solution

If you are running NGINX Plus R33 and earlier or if you still need the njs-based solution, refer to the Legacy njs-based Keycloak Guide for details. The solution uses the nginx-openid-connect GitHub repository and NGINX JavaScript files.

See Also

• NGINX Plus Native OIDC Module Reference documentation

• Release Notes for NGINX Plus R36

Revision History

• Version 3 (November 2025) – Updated for NGINX Plus R36; added front-channel logout support (frontchannel_logout_uri), PKCE configuration (pkce directive), and the client_secret_post token endpoint authentication method.

• Version 2 (August 2025) – Updated for NGINX Plus R35; added RP‑initiated logout (logout_uri, post_logout_uri, logout_token_hint) and userinfo support.

• Version 1 (March 2025) – Initial version (NGINX Plus Release 34).