oidcSessionCheck

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oidcSessionCheck

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JavaScript library to assist with binding sessions between an OIDC OP and RP

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# OIDC Session Check

JavaScript library to assist with binding sessions between an OIDC OP and RP

## Purpose

When you use [OpenID Connect](https://openid.net/specs/openid-connect-core-1_0.html) to handle authentication in your application, there are two parties involved - the "OpenID Provider" (OP) and the Relying Party (RP).

The OP is a web server, and it handles authenticating the user. Oftentimes, when the user logs into the OP with a browser there is a session created there. The OP will set a cookie in the user's browser, which allows the user to be remembered the next time they visit the OP.

The RP is an application which uses the identity details returned from the OP. Typically, it uses these details to construct its own session. The session at the RP does not normally have any relationship to the session at the OP; if a user logs-out of one, it doesn't normally cause the session to end on the other.

When RP applications are owned by the same organization as the OP, there is often a desire to make the various sessions more closely associated. Doing so presents the user with a seamless experience as they navigate between each app. This library is designed to make that session association easier to establish.

## How it works

The cookie which identifies the session at the OP is assumed to be unavailable to the RP (due to differences in their respective domains). However, there is a mechanism available as part of OIDC which allows that cookie to be used. OIDC works by redirection between the RP and OP - the browser makes a request to the OP's "authorization endpoint"; when finished, the OP redirects the browser back to the RP's "redirect_uri" along with some relevant data. This redirection allows the fundamental "session check" to occur - through it you can compare the details of the session at the RP with the details of the session at the OP.

This redirection needs to be non-intrusive; it shouldn't be noticeable to the user while they are interacting with the RP. The most practical way to accomplish this is to make use of hidden iframes within the RP application. The RP can set the iframe `src` value to be the OP authorization endpoint (along with the other required parameters); when this loads, the OP session cookie will be passed along as per normal browser behavior.

Since this use-case involves simple message passing (with no direct user interaction) there is parameter that is always passed along in the authentication request - `prompt=none`. By including this parameter, the response will either succeed immediately or fail immediately - there won't be any "prompt" for the user to log in or anything else.

Comparing session details can be done in one of two places - either at the OP or the RP. Each choice has advantages and disadvantages. Both approaches involve making a hidden iframe-based request to the authorization endpoint - what distinguishes these approaches is the `response_type` and `id_token_hint` parameters.

### response_type=id_token
If you compare session details at the RP, the authorization request uses `response_type=id_token` to try to get back a new `id_token` value representing the state of the OP session. This is essentially an "implicit" OIDC grant; the result (either a new `id_token` or an error message) will be passed back to the RP redirect URI within the hash fragment (see the specification for [Implicit Flow Authentication Requests](https://openid.net/specs/openid-connect-core-1_0.html#rfc.section.3.2.2.1) for more details). When the current OP session is still valid, the RP can compare the claims from the new `id_token` with the claims from its original `id_token`. The RP can then decide which claim differences matter to it (for example, a different subject), and respond accordingly. This is the default behavior for this library.

### response_type=none
If you compare session details at the OP, the RP has to send along its original `id_token` in the authorization request as the `id_token_hint` parameter. The expectation is that the OP will use the claims from the provided `id_token` and compare them with the details of the OP session (as identified by the OP session cookie which is also included in the authorization request). In this case, the RP does not need any particular information when the session is still valid; as such, the authorization request will include `response_type=none`. Depending on how the OP compares the details, it will either respond with an error such as `login_required` or with no URL parameters at all - indicating that the session is still valid. This is the pattern of session checking [documented for ForgeRock  Access Management](https://backstage.forgerock.com/docs/am/7/oidc1-guide/manage-sessions-openid-connect.html#session_management_state) - although both options will work with ForgeRock Access Management.

Regardless of the approach used, the response from the OP must be read by the redirect_uri page within the iframe. Based on the parameters provided, it must use the [postMessage](https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage) API to communicate the results to the RP parent frame.

### Non-Standard Options Available to Trusted Clients

There are some challenges for clients that have to be overcome when they are operated as a "third-party". A third-party client is one that is hosted in a different domain than the authorization server; this is a very common scenario for OAuth 2 clients. Historically, applications in one domain could embed resources (like iframes and scripts) which reside on other domains and expect that those requests would include whatever cookies have been set for that domain. When used this way, the cookies included in those requests are known as "third-party" cookies. The options described above rely on these types of cookies. Unfortunately for client developers, the assumption that third-party cookies will be included in the silent grant request is no longer always true.

Intelligent Tracking Preventing (or ITP) is a privacy feature of some browsers (initially Safari, increasingly adopted by Firefox and others). It is intended to empower users to prevent major media companies from tracking their behavior across numerous websites. It does this by [requiring explicit consent from the user](https://developer.mozilla.org/en-US/docs/Web/API/Storage_Access_API) following some interaction with elements embedded by those media companies (e.g. a "Like" button). While this feature is great for end-user privacy, it does create some unique challenges for SPA OAuth 2 clients. There is no sensible equivalent to a "Like" button for an OAuth 2 authorization server to provide for its third-party clients; therefore there is no easy way to get consent from the user to perform silent grants. Ultimately this means that silent grants which rely on third-party cookies will be blocked by this browser behavior. So, what can be done about it?

If a client application is created by the same organization that owns the authorization server, then it may be considered "trusted". This means that it may be able to do things such as [use implied consent for the scopes it requests](https://backstage.forgerock.com/docs/am/7.1/oauth2-guide/allowing-clients-to-skip-consent.html#allowing-clients-to-skip-consent) rather than having to get explicit permission from the user. The reason this is acceptable is because the authorization server trusts this client to not abuse the authority it has been given over the user's resources. For the same reason, the authorization server can choose to enable non-standard features that rely on having this implied authority. These types of features may allow the client developer to overcome some of the limitations imposed by the browser on third-party clients.

> Note that there is a somewhat unexpected combination of scenarios at play here - a client application that is owned and operated by the same organization that owns the authorization server, but is hosted in a separate domain from that same authorization server. This might occur when the hosting environment for the AS is isolated from the hosting environment from the client, and DNS aliasing isn't available as a solution.

As an example of this, consider the ForgeRock Access Manager ("AM") endpoint for [Validating Sessions Using REST](https://backstage.forgerock.com/docs/am/7.1/sessions-guide/managing-sessions-REST.html#rest-api-token-validation). This endpoint takes the AM session token and returns whether or not the session is valid. If it is valid, it resets the idle timeout and returns some basic information about the session. Note that this request is only possible if the caller has the AM session token; this is a highly-sensitive value that represents the user's full session. Any action that can be taken by the user can be taken by the bearer of this token. For this reason, only clients that are fully trusted by the authorization server should have access to this value. It's important to note that this method does not rely on cookies; instead, it passes the session token as a custom header. This is why third-party cookie restrictions do not prevent it from working.

A trusted client can choose to use this method for session status checking and single log-out instead of the standard "silent grant" approaches described above. To do so, AM must be configured to include the session token as an extra claim within the id_token (but only for trusted clients). This can be done using an [OIDC Claims Script](https://backstage.forgerock.com/docs/am/7.1/oidc1-guide/scripted-oidc-claims.html#scripted-oidc-claims). Here is a sample modification of the default Groovy OIDC claims script which adds the session token. It will only add the "sso_token" claim for clients which have requested it (using the "sso_token" scope) and is only available for those clients which been configured with the custom property `allow_sso_token=true` :

```groovy
def getSSOTokenForTrustedClients = {
  if (session && clientProperties.get("customProperties").get("allow_sso_token") == "true") {
    return session.getTokenID().toString();
  } else {
    return null;
  }
}

claimAttributes = [
        "email": userProfileClaimResolver.curry("mail"),
        // others removed for brevity...
        "sso_token":  { claim, identity -> [ "sso_token" : getSSOTokenForTrustedClients() ] }
]

scopeClaimsMap = [
        "email": [ "email" ],
        // others removed for brevity...
        "sso_token": [ "sso_token" ]
]
```

> Note - for this script to work, the Java class `com.iplanet.sso.providers.dpro.SSOTokenIDImpl` must be added to the whitelist for OIDC_CLAIMS engine configuration. See [Script Engine Security](https://backstage.forgerock.com/docs/am/7.1/scripting-guide/script-engine-security.html) for more details. In the ForgeRock Identity Cloud, this should already be configured for you. You also need to enable "Always Return Claims in ID Tokens" (Realms > Realm Name > Services > OAuth2 Provider > Advanced OpenID Connect). Finally, be sure you have added "iPlanetDirectoryPro" (or whatever you are using for the ssoTokenName) to the list of accepted headers for your CORS service.

Using this feature, you can retain a full SSO experience in your cross-domain, cookie-restricted application.

## Using this library

This library automates the message passing between your RP and the OP. It allows you to easily monitor the state of the OP session - you simply need to provide a few details about your operating environment and decide when you want those checks to be made.

The "SessionCheck" module can be loaded in several ways:
 - using a global variable by directly including a script tag: `<script src="sessionCheckGlobal.js"></script>`
 - using CommonJS modules: `var SessionCheck = require('sessionCheck');`

*Setting up the environment:*
```JavaScript
    var sessionCheck = new SessionCheck({

// optional, used with `response_type=id_token` and ForgeRock-method to enforce subject consistency
        subject: loggedInUsername,

// required function to handle invalid sessions. Take whatever appropriate measures for your app here.
        // reason could be interaction_required, login_required, subject_mismatch, nonce_mismatch or possibly other responses from the OP
        // request_check_count is an integer representing the number of session check requests that have been attempted, as of this invocation
        invalidSessionHandler: function (reason, request_check_count) {
            logoutFromRP();
        },

// optional. Only called once, when the first successful session check occurs. May be useful for delayed-loading of app code
        initialSessionSuccessHandler: function () {
            // do something interesting once you know the session is valid, such as loading more app code
        },

// optional. Only called when using `responseType=id_token`
        // claims is the detailed claim information obtained from the latest id_token response
        // request_check_count is an integer representing the number of session check requests that have been attempted, as of this invocation
        sessionClaimsHandler: function (claims, request_check_count) {
            // do something interesting with the new claims, like compare them to old claims for meaningful differences to the session
        },

// optional, defaults to 5 seconds
        cooldownPeriod: 5,

// ssoToken, ssoTokenName and amUrl are ForgeRock-only method for session checking available to trusted clients
        ssoToken: sso_token,

// iPlanetDirectoryPro is the default; in ForgeRock Identity Cloud, it will be the random cookie name used for the session
        ssoTokenName: "iPlanetDirectoryPro",

// using "amUrl" instead of "opUrl" to indicate that we are using the ForgeRock-only method
        amUrl: "https://default.iam.example.com/am/json/realms/root",

// below options use OIDC standard methods for session checking, involving hidden iframes and (possibly third-party) cookies.
        clientId: "myRP",
        opUrl: "https://login.example.com/oauth2/authorize",

// optional
        redirectUri: "sessionCheck.html",

// optional, defaults to "id_token". Other valid value is "none"
        responseType: "id_token",

// optional - only used with `responseType=id_token`
        scope: "openid",

// required if using `response_type=none`. If used with `response_type=id_token`, will be used to enforce subject consistency
        idToken: current_id_token,

});
```
*Examples for when to check the session:*

```JavaScript
    // check with various events based on user interaction:
    document.addEventListener("click", function () {
        sessionCheck.triggerSessionCheck();
    });
    document.addEventListener("keypress", function () {
        sessionCheck.triggerSessionCheck();
    });

// check every minute (not recommended)
    setInterval(function () {
        sessionCheck.triggerSessionCheck();
    }, 60000);
```

*Details you need to provide:*

- invalidSessionHandler - function to be called once any problem with the session is detected, with reason for the invalid sessions and request count included
 - subject [optional] - Only used with `responseType=id_token` and ForgeRock-only methods. The user currently logged into the RP. If not supplied, subject changes won't trigger the invalidSessionHandler
 - sessionClaimsHandler [optional] - function to be called after every successful session check, with latest claims and request count included. Only used with `responseType=id_token`.
 - initialSessionSuccessHandler [optional] - optional function to be called after the first successful session check request.
 - cooldownPeriod [default: 5] - Minimum time (in seconds) between requests to the opUrl

ForgeRock-specific options:
 - ssoToken - String representing the user's session within AM. Likely made available as a custom idToken claim
 - ssoTokenName - Name of the session token. Defaults to iPlanetDirectoryPro, but often [changed to a different value](https://backstage.forgerock.com/docs/am/7.1/security-guide/change-name-of-SSO-cookie.html).
 - amUrl - The full URL (including path to the base of the realm) of the AM server that issued the ssoToken

OIDC-standard options:
 - clientId - The id of this RP client within the OP
 - opUrl - Full URL to the OP Authorization Endpoint
 - responseType [default: id_token] - One of either "id_token" or "none". See "How it works" above for the full description of each.
 - idToken - The current id_token value from your original OIDC authorization request. Required if using `responseType=none`
 - redirectUri [default: sessionCheck.html] - The redirect uri registered in the OP for session-checking purposes
 - scope [default: openid] - OIDC scope names (space separated) to be requested. Only used with `responseType=id_token`.

This library requires that your user is already authenticated prior to creating an instance of it. If you are using `responseType=none`, you *must* provide the current `id_token` associated with the current authenticated session. If you are using `responseType=id_token`, you can provide the current "subject" of the current session, and this will be checked against the "subject" claim within the id_token that is returned by the OP. If they don't match, it is assumed that the OP and RP sessions are out of sync, and that will trigger the `invalidSessionHandler` with the reason "subject_mismatch".

The `invalidSessionHandler` will be called whenever there is a problem detected from the OP response. The intent for this handler is for you to trigger a local log-out event, so that the current RP session is terminated. This will likely result in an interactive OIDC-based redirection to the OP so as to obtain a new RP session. It will be given the reason for the failure, along with the number of attempts that have so far been made to check the session. You might find using these details to handle specific cases can result in a better user-experience for those cases.

If you are using `responseType=id_token`, the `sessionClaimsHandler` will be called every time the session check occurs. It will include the claims from the new id_token. The intent for this handler is to allow you to respond to various claims that might be included in the id_token - for example, you could use the "exp" claim to warn the user when their session will end. This handler is optional.

The `initialSessionSuccessHandler` will be called once, upon the first successful session check request. This can be a useful function to define if you don't want to load any main application code until after you have established that the current session is valid.

If you are using a standard option, you will need to make sure the redirect_uri used for this is registered with the OP. By default, you can use the included [sessionCheck.html](./sessionCheck.html) as the uri to register. Whatever you choose to use, be sure the [sessionCheckFrame.js](./sessionCheckFrame.js) code is included within it.

It is up to you to decide how frequently and in which circumstances you want to check the OP for session status changes. The "cooldownPeriod" setting determines the maximum frequency you want to check the OP. Regardless of how many times you call `triggerSessionCheck()` within that period, it will only be checked once. As a result, you can call this using any combination of events without worrying about flooding the OP with requests.

*Cleaning up the environment*

Once the SessionCheck instance is no longer needed you should `destroy()` and nullify the instance to garbage collect the instance, the related iframe, and global event handlers.

```javascript
    var sessionCheck = new SessionCheck(config);
    // use sessionCheck... then when you're done with it...
    sessionCheck.destroy();
    sessionCheck = null;
```

## License

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