SSO protocols

This section discusses authentication protocols, the Keycloak authentication server and how applications, secured by the Keycloak authentication server, interact with these protocols.

OpenID Connect

OpenID Connect (OIDC) is an authentication protocol that is an extension of OAuth 2.0.

OAuth 2.0 is a framework for building authorization protocols and is incomplete. OIDC, however, is a full authentication and authorization protocol that uses the Json Web Token (JWT) standards. The JWT standards define an identity token JSON format and methods to digitally sign and encrypt data in a compact and web-friendly way.

In general, OIDC implements two use cases. The first case is an application requesting that a Keycloak server authenticates a user. Upon successful login, the application receives an identity token and an access token. The identity token contains user information including user name, email, and profile information. The realm digitally signs the access token which contains access information (such as user role mappings) that applications use to determine the resources users can access in the application.

The second use case is a client accessing remote services.

The client requests an access token from Keycloak to invoke on remote services on behalf of the user.
Keycloak authenticates the user and asks the user for consent to grant access to the requesting client.
The client receives the access token which is digitally signed by the realm.
The client makes REST requests on remote services using the access token.
The remote REST service extracts the access token.
The remote REST service verifies the tokens signature.
The remote REST service decides, based on access information within the token, to process or reject the request.

OIDC auth flows

OIDC has several methods, or flows, that clients or applications can use to authenticate users and receive identity and access tokens. The method depends on the type of application or client requesting access.

Authorization Code Flow

The Authorization Code Flow is a browser-based protocol and suits authenticating and authorizing browser-based applications. It uses browser redirects to obtain identity and access tokens.

A user connects to an application using a browser. The application detects the user is not logged into the application.
The application redirects the browser to Keycloak for authentication.
The application passes a callback URL as a query parameter in the browser redirect. Keycloak uses the parameter upon successful authentication.
Keycloak authenticates the user and creates a one-time, short lived, temporary code.
Keycloak redirects to the application using the callback URL and adds the temporary code as a query parameter in the callback URL.
The application extracts the temporary code and makes a background REST invocation to Keycloak to exchange the code for an identity and access and refresh token. To prevent replay attacks, the temporary code cannot be used more than once.

A system is vulnerable to a stolen token for the lifetime of that token. For security and scalability reasons, access tokens are generally set to expire quickly so subsequent token requests fail. If a token expires, an application can obtain a new access token using the additional refresh token sent by the login protocol.

Confidential clients provide client secrets when they exchange the temporary codes for tokens. Public clients are not required to provide client secrets. Public clients are secure when HTTPS is strictly enforced and redirect URIs registered for the client are strictly controlled. HTML5/JavaScript clients have to be public clients because there is no way to securely transmit the client secret to HTML5/JavaScript clients. For more details, see the Managing Clients chapter.

Keycloak also supports the Proof Key for Code Exchange specification.

Implicit Flow

The Implicit Flow is a browser-based protocol. It is similar to the Authorization Code Flow but with fewer requests and no refresh tokens.

The possibility exists of access tokens leaking in the browser history when tokens are transmitted via redirect URIs (see below).

Also, this flow does not provide clients with refresh tokens. Therefore, access tokens have to be long-lived or users have to re-authenticate when they expire.

We do not advise using this flow. This flow is supported because it is in the OIDC and OAuth 2.0 specification.

The protocol works as follows:

A user connects to an application using a browser. The application detects the user is not logged into the application.
The application redirects the browser to Keycloak for authentication.
The application passes a callback URL as a query parameter in the browser redirect. Keycloak uses the query parameter upon successful authentication.
Keycloak authenticates the user and creates an identity and access token. Keycloak redirects to the application using the callback URL and additionally adds the identity and access tokens as a query parameter in the callback URL.
The application extracts the identity and access tokens from the callback URL.

Resource owner password credentials grant (Direct Access Grants)

Direct Access Grants are used by REST clients to obtain tokens on behalf of users. It is a HTTP POST request that contains:

The credentials of the user. The credentials are sent within form parameters.
The id of the client.
The clients secret (if it is a confidential client).

The HTTP response contains the identity, access, and refresh tokens.

Client credentials grant

The Client Credentials Grant creates a token based on the metadata and permissions of a service account associated with the client instead of obtaining a token that works on behalf of an external user. Client Credentials Grants are used by REST clients.

See the Service Accounts chapter for more information.

Device authorization grant

This is used by clients running on internet-connected devices that have limited input capabilities or lack a suitable browser.Here’s a brief summary of the protocol:

The application requests Keycloak a device code and a user code. Keycloak creates a device code and a user code. Keycloak returns a response including the device code and the user code to the application.
The application provides the user with the user code and the verification URI.The user accesses a verification URI to be authenticated by using another browser.
The application repeatedly polls Keycloak to find out if the user completed the user authorization.If user authentication is complete, the application exchanges the device code for an identity, access and refresh token.

Client initiated backchannel authentication grant

This feature is used by clients who want to initiate the authentication flow by communicating with the OpenID Provider directly without redirect through the user’s browser like OAuth 2.0’s authorization code grant. Here’s a brief summary of the protocol:

The client requests Keycloak an auth_req_id that identifies the authentication request made by the client. Keycloak creates the auth_req_id.
After receiving this auth_req_id, this client repeatedly needs to poll Keycloak to obtain an Access Token, Refresh Token and ID Token from Keycloak in return for the auth_req_id until the user is authenticated.

An administrator can configure Client Initiated Backchannel Authentication (CIBA) related operations as CIBA Policy per realm.

Also please refer to other places of Keycloak documentation like Backchannel Authentication Endpoint section of Securing Applications and Services Guide and Client Initiated Backchannel Authentication Grant section of Securing Applications and Services Guide.

CIBA Policy

An administrator carries out the following operations on the Admin Console :

Open the Authentication → CIBA Policy tab.
Configure items and click Save.

The configurable items and their description follow.

Configuration	Description
Backchannel Token Delivery Mode	Specifying how the CD (Consumption Device) gets the authentication result and related tokens. There are three modes, "poll", "ping" and "push". Keycloak only supports "poll". The default setting is "poll". This configuration is required. For more details, see CIBA Specification.
Expires In	The expiration time of the "auth_req_id" in seconds since the authentication request was received. The default setting is 120. This configuration is required. For more details, see CIBA Specification.
Interval	The interval in seconds the CD (Consumption Device) needs to wait for between polling requests to the token endpoint. The default setting is 5. This configuration is optional. For more details, see CIBA Specification.
Authentication Requested User Hint	The way of identifying the end-user for whom authentication is being requested. The default setting is "login_hint". There are three modes, "login_hint", "login_hint_token" and "id_token_hint". Keycloak only supports "login_hint". This configuration is required. For more details, see CIBA Specification.

Configuration

Description

Backchannel Token Delivery Mode

Specifying how the CD (Consumption Device) gets the authentication result and related tokens. There are three modes, "poll", "ping" and "push". Keycloak only supports "poll". The default setting is "poll". This configuration is required. For more details, see CIBA Specification.

Expires In

The expiration time of the "auth_req_id" in seconds since the authentication request was received. The default setting is 120. This configuration is required. For more details, see CIBA Specification.

Interval

The interval in seconds the CD (Consumption Device) needs to wait for between polling requests to the token endpoint. The default setting is 5. This configuration is optional. For more details, see CIBA Specification.

Authentication Requested User Hint

The way of identifying the end-user for whom authentication is being requested. The default setting is "login_hint". There are three modes, "login_hint", "login_hint_token" and "id_token_hint". Keycloak only supports "login_hint". This configuration is required. For more details, see CIBA Specification.

Provider Setting

The CIBA grant uses the following two providers.

Authentication Channel Provider : provides the communication between Keycloak and the entity that actually authenticates the user via AD (Authentication Device).
User Resolver Provider : get UserModel of Keycloak from the information provided by the client to identify the user.

Keycloak has both default providers. However, the administrator needs to set up Authentication Channel Provider like this:

kc.[sh|bat] start --spi-ciba-auth-channel-ciba-http-auth-channel-http-authentication-channel-uri=https://backend.internal.example.com

The configurable items and their description follow.

Configuration	Description
http-authentication-channel-uri	Specifying URI of the entity that actually authenticates the user via AD (Authentication Device).

Configuration

Description

http-authentication-channel-uri

Specifying URI of the entity that actually authenticates the user via AD (Authentication Device).

Authentication Channel Provider

CIBA standard document does not specify how to authenticate the user by AD. Therefore, it might be implemented at the discretion of products. Keycloak delegates this authentication to an external authentication entity. To communicate with the authentication entity, Keycloak provides Authentication Channel Provider.

Its implementation of Keycloak assumes that the authentication entity is under the control of the administrator of Keycloak so that Keycloak trusts the authentication entity. It is not recommended to use the authentication entity that the administrator of Keycloak cannot control.

Authentication Channel Provider is provided as SPI provider so that users of Keycloak can implement their own provider in order to meet their environment. Keycloak provides its default provider called HTTP Authentication Channel Provider that uses HTTP to communicate with the authentication entity.

If a user of Keycloak user want to use the HTTP Authentication Channel Provider, they need to know its contract between Keycloak and the authentication entity consisting of the following two parts.

Authentication Delegation Request/Response: Keycloak sends an authentication request to the authentication entity.
Authentication Result Notification/ACK: The authentication entity notifies the result of the authentication to Keycloak.

Authentication Delegation Request/Response consists of the following messaging.

Authentication Delegation Request: The request is sent from Keycloak to the authentication entity to ask it for user authentication by AD.

POST [delegation_reception]

Headers

Name	Value	Description
Content-Type	application/json	The message body is json formatted.
Authorization	Bearer [token]	The [token] is used when the authentication entity notifies the result of the authentication to Keycloak.

Name

Value

Description

Content-Type

application/json

The message body is json formatted.

Authorization

Bearer [token]

The [token] is used when the authentication entity notifies the result of the authentication to Keycloak.

Parameters

Type	Name	Description
Path	delegation_reception	The endpoint provided by the authentication entity to receive the delegation request

Type

Name

Description

Path

delegation_reception

The endpoint provided by the authentication entity to receive the delegation request

Body

Name	Description
login_hint	It tells the authentication entity who is authenticated by AD. By default, it is the user’s "username". This field is required and was defined by CIBA standard document.
scope	It tells which scopes the authentication entity gets consent from the authenticated user. This field is required and was defined by CIBA standard document.
is_consent_required	It shows whether the authentication entity needs to get consent from the authenticated user about the scope. This field is required.
binding_message	Its value is intended to be shown in both CD and AD’s UI to make the user recognize that the authentication by AD is triggered by CD. This field is optional and was defined by CIBA standard document.
acr_values	It tells the requesting Authentication Context Class Reference from CD. This field is optional and was defined by CIBA standard document.

Name

Description

login_hint

It tells the authentication entity who is authenticated by AD.
By default, it is the user’s "username".
This field is required and was defined by CIBA standard document.

scope

It tells which scopes the authentication entity gets consent from the authenticated user.
This field is required and was defined by CIBA standard document.

is_consent_required

It shows whether the authentication entity needs to get consent from the authenticated user about the scope.
This field is required.

binding_message

Its value is intended to be shown in both CD and AD’s UI to make the user recognize that the authentication by AD is triggered by CD.
This field is optional and was defined by CIBA standard document.

acr_values

It tells the requesting Authentication Context Class Reference from CD.
This field is optional and was defined by CIBA standard document.

Authentication Delegation Response

The response is returned from the authentication entity to Keycloak to notify that the authentication entity received the authentication request from Keycloak.

Responses

HTTP Status Code	Description
201	It notifies Keycloak of receiving the authentication delegation request.

Authentication Result Notification/ACK consists of the following messaging.

Authentication Result Notification: The authentication entity sends the result of the authentication request to Keycloak.

POST /realms/[realm]/protocol/openid-connect/ext/ciba/auth/callback

Headers

Name	Value	Description
Content-Type	application/json	The message body is json formatted.
Authorization	Bearer [token]	The [token] must be the one the authentication entity has received from Keycloak in Authentication Delegation Request.

Name

Value

Description

Content-Type

application/json

The message body is json formatted.

Authorization

Bearer [token]

The [token] must be the one the authentication entity has received from Keycloak in Authentication Delegation Request.

Parameters

Type	Name	Description
Path	realm	The realm name

Type

Name

Description

Path

realm

The realm name

Body

Name	Description
status	It tells the result of user authentication by AD. It must be one of the following status. SUCCEED : The authentication by AD has been successfully completed. UNAUTHORIZED : The authentication by AD has not been completed. CANCELLED : The authentication by AD has been cancelled by the user.

Name

Description

status

It tells the result of user authentication by AD.
It must be one of the following status.
SUCCEED : The authentication by AD has been successfully completed.
UNAUTHORIZED : The authentication by AD has not been completed.
CANCELLED : The authentication by AD has been cancelled by the user.

Authentication Result ACK

The response is returned from Keycloak to the authentication entity to notify Keycloak received the result of user authentication by AD from the authentication entity.

Responses

HTTP Status Code	Description
200	It notifies the authentication entity of receiving the notification of the authentication result.

User Resolver Provider

Even if the same user, its representation may differ in each CD, Keycloak and the authentication entity.

For CD, Keycloak and the authentication entity to recognize the same user, this User Resolver Provider converts their own user representations among them.

User Resolver Provider is provided as SPI provider so that users of Keycloak can implement their own provider in order to meet their environment. Keycloak provides its default provider called Default User Resolver Provider that has the following characteristics.

Only support login_hint parameter and is used as default.
username of UserModel in Keycloak is used to represent the user on CD, Keycloak and the authentication entity.

OIDC Logout

OIDC has four specifications relevant to logout mechanisms. These specifications are in draft status:

Again since all of this is described in the OIDC specification we will only give a brief overview here.

Session Management

This is a browser-based logout. The application obtains session status information from Keycloak at a regular basis. When the session is terminated at Keycloak the application will notice and trigger it’s own logout.

RP-Initiated Logout

This is also a browser-based logout where the logout starts by redirecting the user to a specific endpoint at Keycloak. This redirect usually happens when the user clicks the Log Out link on the page of some application, which previously used Keycloak to authenticate the user.

Once the user is redirected to the logout endpoint, Keycloak is going to send logout requests to clients to let them to invalidate their local user sessions, and potentially redirect the user to some URL once the logout process is finished. The user might be optionally requested to confirm the logout in case the id_token_hint parameter was not used. After logout, the user is automatically redirected to the specified post_logout_redirect_uri as long as it is provided as a parameter. Note that you need to include either the client_id or id_token_hint parameter in case the post_logout_redirect_uri is included. Also the post_logout_redirect_uri parameter needs to match one of the Valid Post Logout Redirect URIs specified in the client configuration.

Depending on the client configuration, logout requests can be sent to clients through the front-channel or through the back-channel. For the frontend browser clients, which rely on the Session Management described in the previous section, Keycloak does not need to send any logout requests to them; these clients automatically detect that SSO session in the browser is logged out.

Frontchannel Logout

To configure clients to receive logout requests through the front-channel, look at the Front-Channel Logout client setting. When using this method, consider the following:

Logout requests sent by Keycloak to clients rely on the browser and on embedded iframes that are rendered for the logout page.
By being based on iframes, front-channel logout might be impacted by Content Security Policies (CSP) and logout requests might be blocked.
If the user closes the browser prior to rendering the logout page or before logout requests are actually sent to clients, their sessions at the client might not be invalidated.

Consider using Back-Channel Logout as it provides a more reliable and secure approach to log out users and terminate their sessions on the clients.

If the client is not enabled with front-channel logout, then Keycloak is going to try first to send logout requests through the back-channel using the Back-Channel Logout URL. If not defined, the server is going to fall back to using the Admin URL.

Backchannel Logout

This is a non browser-based logout that uses direct backchannel communication between Keycloak and clients. Keycloak sends a HTTP POST request containing a logout token to all clients logged into Keycloak. These requests are sent to a registered backchannel logout URLs at Keycloak and are supposed to trigger a logout at client side.

Keycloak server OIDC URI endpoints

The following is a list of OIDC endpoints that Keycloak publishes. These endpoints can be used when a non-Keycloak client adapter uses OIDC to communicate with the authentication server. They are all relative URLs. The root of the URL consists of the HTTP(S) protocol, hostname, and optionally the path: For example

https://localhost:8080

/realms/{realm-name}/protocol/openid-connect/auth: Used for obtaining a temporary code in the Authorization Code Flow or obtaining tokens using the Implicit Flow, Direct Grants, or Client Grants.
/realms/{realm-name}/protocol/openid-connect/token: Used by the Authorization Code Flow to convert a temporary code into a token.
/realms/{realm-name}/protocol/openid-connect/logout: Used for performing logouts.
/realms/{realm-name}/protocol/openid-connect/userinfo: Used for the User Info service described in the OIDC specification.
/realms/{realm-name}/protocol/openid-connect/revoke: Used for OAuth 2.0 Token Revocation described in RFC7009.
/realms/{realm-name}/protocol/openid-connect/certs: Used for the JSON Web Key Set (JWKS) containing the public keys used to verify any JSON Web Token (jwks_uri)
/realms/{realm-name}/protocol/openid-connect/auth/device: Used for Device Authorization Grant to obtain a device code and a user code.
/realms/{realm-name}/protocol/openid-connect/ext/ciba/auth: This is the URL endpoint for Client Initiated Backchannel Authentication Grant to obtain an auth_req_id that identifies the authentication request made by the client.
/realms/{realm-name}/protocol/openid-connect/logout/backchannel-logout: This is the URL endpoint for performing backchannel logouts described in the OIDC specification.

In all of these, replace {realm-name} with the name of the realm.

SAML

SAML 2.0 is a similar specification to OIDC but more mature. It is descended from SOAP and web service messaging specifications so is generally more verbose than OIDC. SAML 2.0 is an authentication protocol that exchanges XML documents between authentication servers and applications. XML signatures and encryption are used to verify requests and responses.

In general, SAML implements two use cases.

The first use case is an application that requests the Keycloak server authenticates a user. Upon successful login, the application will receive an XML document. This document contains an SAML assertion that specifies user attributes. The realm digitally signs the the document which contains access information (such as user role mappings) that applications use to determine the resources users are allowed to access in the application.

The second use case is a client accessing remote services. The client requests a SAML assertion from Keycloak to invoke on remote services on behalf of the user.

SAML bindings

Keycloak supports three binding types.

Redirect binding

Redirect binding uses a series of browser redirect URIs to exchange information.

A user connects to an application using a browser. The application detects the user is not authenticated.
The application generates an XML authentication request document and encodes it as a query parameter in a URI. The URI is used to redirect to the Keycloak server. Depending on your settings, the application can also digitally sign the XML document and include the signature as a query parameter in the redirect URI to Keycloak. This signature is used to validate the client that sends the request.
The browser redirects to Keycloak.
The server extracts the XML auth request document and verifies the digital signature, if required.
The user enters their authentication credentials.
After authentication, the server generates an XML authentication response document. The document contains a SAML assertion that holds metadata about the user, including name, address, email, and any role mappings the user has. The document is usually digitally signed using XML signatures, and may also be encrypted.
The XML authentication response document is encoded as a query parameter in a redirect URI. The URI brings the browser back to the application. The digital signature is also included as a query parameter.
The application receives the redirect URI and extracts the XML document.
The application verifies the realm’s signature to ensure it is receiving a valid authentication response. The information inside the SAML assertion is used to make access decisions or display user data.

POST binding

POST binding is similar to Redirect binding but POST binding exchanges XML documents using POST requests instead of using GET requests. POST Binding uses JavaScript to make the browser send a POST request to the Keycloak server or application when exchanging documents. HTTP responds with an HTML document which contains an HTML form containing embedded JavaScript. When the page loads, the JavaScript automatically invokes the form.

POST binding is recommended due to two restrictions:

Security — With Redirect binding, the SAML response is part of the URL. It is less secure as it is possible to capture the response in logs.
Size — Sending the document in the HTTP payload provides more scope for large amounts of data than in a limited URL.

ECP

Enhanced Client or Proxy (ECP) is a SAML v.2.0 profile which allows the exchange of SAML attributes outside the context of a web browser. It is often used by REST or SOAP-based clients.

Keycloak Server SAML URI Endpoints

Keycloak has one endpoint for all SAML requests.

http(s)://authserver.host/realms/{realm-name}/protocol/saml

All bindings use this endpoint.

OpenID Connect compared to SAML

The following lists a number of factors to consider when choosing a protocol.

For most purposes, Keycloak recommends using OIDC.

OIDC

OIDC is specifically designed to work with the web.
OIDC is suited for HTML5/JavaScript applications because it is easier to implement on the client side than SAML.
OIDC tokens are in the JSON format which makes them easier for Javascript to consume.
OIDC has features to make security implementation easier. For example, see the iframe trick that the specification uses to determine a users login status.

SAML

SAML is designed as a layer to work on top of the web.
SAML can be more verbose than OIDC.
Users pick SAML over OIDC because there is a perception that it is mature.
Users pick SAML over OIDC existing applications that are secured with it.

Docker registry v2 authentication

Docker authentication is disabled by default. To enable docker authentication, see the Enabling and disabling features guide.

Docker Registry V2 Authentication is a protocol, similar to OIDC, that authenticates users against Docker registries. Keycloak’s implementation of this protocol lets Docker clients use a Keycloak authentication server authenticate against a registry. This protocol uses standard token and signature mechanisms but it does deviate from a true OIDC implementation. It deviates by using a very specific JSON format for requests and responses as well as mapping repository names and permissions to the OAuth scope mechanism.

Docker authentication flow

The authentication flow is described in the Docker API documentation. The following is a summary from the perspective of the Keycloak authentication server:

Perform a docker login.
The Docker client requests a resource from the Docker registry. If the resource is protected and no authentication token is in the request, the Docker registry server responds with a 401 HTTP message with some information on the permissions that are required and the location of the authorization server.
The Docker client constructs an authentication request based on the 401 HTTP message from the Docker registry. The client uses the locally cached credentials (from the docker login command) as part of the HTTP Basic Authentication request to the Keycloak authentication server.
The Keycloak authentication server attempts to authenticate the user and return a JSON body containing an OAuth-style Bearer token.
The Docker client receives a bearer token from the JSON response and uses it in the authorization header to request the protected resource.
The Docker registry receives the new request for the protected resource with the token from the Keycloak server. The registry validates the token and grants access to the requested resource (if appropriate).

Keycloak does not create a browser SSO session after successful authentication with the Docker protocol. The browser SSO session does not use the Docker protocol as it cannot refresh tokens or obtain the status of a token or session from the Keycloak server; therefore a browser SSO session is not necessary. For more details, see the transient session section.

Keycloak Docker Registry v2 Authentication Server URI Endpoints

Keycloak has one endpoint for all Docker auth v2 requests.

http(s)://authserver.host/realms/{realm-name}/protocol/docker-v2