12 April, 2020

SAML

The Liferay DXP’s SAML (Security Assertion Markup Language) adapter lets you execute Single Sign On (SSO) and Single Log Off (SLO) in your deployment. Each Liferay DXP instance serves as either the Service Provider (SP) or the Identity Provider (IdP). This article provides the conceptual framework for Liferay DXP’s SSO solution.
  • Single Sign On
    • Identity Provider initiated SSO
    • Service Provider initiated SSO
  • Single Log Off
    • Identity Provider initiated SLO
    • Service Provider initiated SLO
Below is background on how SAML works. To jump right to its configuration, see the next article on Setting Up SAML for instructions on using the SAML adapter. Use the instructions to make the conceptual magic from this article come to life!

Important SAML URLs

For reference, here are a few important SAML URLs.
This URL is the default location of Liferay DXP’s metadata XML file:
[host]:[port]/c/portal/saml/metadata
Note that when configuring SAML for Liferay DXP, no importing of SAML certificates is required. Liferay DXP reads certificates from the SAML metadata XML file. If you want a third-party application like Salesforce to read a Liferay SAML certificate, you can export the Liferay DXP certificate from the keystore. The default keystore file is [Liferay Home]/data/keystore.jks. The exported certificate can be imported by a third-party application like Salesforce.

Single Sign On

Both the IdP and the SP can initiate the Single Sign On process, and the SSO flow is different depending on each one. Consider IdP initiated SSO first.

Identity Provider Initiated SSO

Sometimes a user enters the SSO cycle by sending a request directly from the browser to the IdP.
saml-idp-initiated-sso.png
Figure 1: Identity Provider Initiated SSO

The SSO Request to the IdP

If Liferay DXP is the IdP, the IdP initiated SSO URL
  • Must specify the path as /c/portal/saml/sso.
  • Must include the entityId parameter which is the identifier to a previously configured Service Provider Connection (SPC).
  • May include a RelayState parameter which contains a URL encoded value to which the user will be redirected upon successful authentication. This URL should point to a location on the desired SPC (according to the SAML 2.0 standards section 3.4.3, this value must not exceed 80 bytes in length). It is useful to specify a landing page after SSO has been executed.
For non-Liferay DXP IdPs (Siteminder, ADFS, etc.), consult the vendor’s documentation on constructing IdP initiated SSO URLs.
If the IdP determines that the user isn’t authenticated, it prompts the user with the appropriate login screen.

The SSO Response from the IdP

Upon successful authentication the IdP constructs a SAML Response. It includes attribute statements configured in the designated Service Provider Connection (SPC; see the next article on setting up the SPC in Liferay DXP’s SAML adapter).
The IdP sends the response to the Assertion Consumer Service URL using HTTP-POST or HTTP-Redirect. HTTP-POST is preferred because it reduces the risk that the URL is too long for a browser to handle. Using HTTP-POST, the request contains two parameters:
SAMLResponse
and
RelayState

The SP Processes the SSO Response

The SP validates and processes the SAML Response. Liferay DXP’s SAML solution requires SAMLResponse messages to be signed. This signature process ensures proper identification for the IdP and prevents potential SAML Response spoofing.
  • If one Liferay DXP instance is the IdP and another is the SP, make sure the SAML metadata XML file imported into the Liferay DXP SP contains the IdP’s certificate.
  • If Liferay DXP is the IdP and another application is the SP, export the certificate from the Liferay DXP IdP and import it into the SP’s certificate store.
If a RelayState is included in the SAML Response, the user is redirected to it. Otherwise the home page of the SP is served.

Service Provider Initiated SSO

saml-sp-initiated-sso.png
Figure 2: Service Provider Initiated SSO

The SSO Request to the SP

When the user’s browser requests a protected resource or sign on URL on the SP, it triggers the SP initiated SSO process. When Liferay DXP is the SAML SP, SSO is initiated either by requesting /c/portal/login URL or a protected resource that requires authentication (for example, a document that is not viewable by the Guest role). If the user requests a protected resource, its URL is recorded in the RelayState parameter. If the user requested /c/portal/login, the RelayState can be set by providing the redirect parameter. Otherwise, if the portal property auth.forward.by.last.path is set to true, the last accessed path is set as the RelayState. For non-Liferay DXP SPs, consult the vendor documentation on initiating SSO.

The AuthnRequest to the IdP

The SP looks up the IdP’s Single Sign On service URL and sends an AuthnRequest. When Liferay DXP is the SP it looks up the configured SAML Identity Provider Connection and sends a SAML AuthnRequest to the IdP’s Single Sign On service URL as defined in the SAML metadata XML document. Liferay DXP supports sending and receiving the AuthnRequest using HTTP-Post or HTTP-Redirect binding. HTTP-Post is preferred.
If the user doesn’t have an active session or if ForceAuthn was requested by the SP, the user must authenticate by providing his or her credentials. When Liferay DXP is the IdP, authentication occurs in the Login Portlet. Liferay DXP decodes and verifies the AuthnRequest before requesting the user to authenticate.

The SSO Response from the IdP

After authentication a SAML Response is constructed, sent to the Assertion Consumer Service URL of the SP, and verified.
When Liferay DXP is configured as the IdP, any attributes configured on the Service Provider Connection are included in the response as attribute statements. The Assertion Consumer Service URL is looked up from the SAML metadata XML of the SP. The response is sent using HTTP-Post or HTTP-redirect binding. The IdP automatically makes this choice based on the SP metadata. HTTP-Post binding is preferred and used when available. HTTP-Redirect binding is fragile because the signature and included assertions often make the URL too long for browsers.
When Liferay DXP is configured as the SP, any response and assertion signatures are verified. Liferay DXP requires the sender to be authenticated. This is done via whole message signature from the issuing IdP. Any responses missing the signature are considered unauthenticated and the response is rejected. The Response can be received via HTTP-Post binding or HTTP-redirect binding. HTTP-Post binding is preferred for the reasons mentioned in the previous section. For non-Liferay DXP SP or IdP vendors, consult their documentation.
The user is redirected to the requested resource or to the URL contained in the RelayState parameter (for example, the last page the user accessed before initiating SSO).

Single Log Off

The Single Log Off request is sent from the user’s browser to either the IdP or to a SP, and the SLO flow differs in each case. First consider IdP initiated SLO.

Identity Provider Initiated SLO

saml-idp-initiated-slo.png
Figure 3: Identity Provider Initiated SLO

The SLO Request to the IdP

An IdP initiated SLO request is a SLO request sent directly to the IdP by the user’s browser. When Liferay DXP serves as the IdP, the IdP initiated SSO URL must specify the URL path as
/c/portal/logout
If the user is signed on to any configured SP, the SAML plugin takes over the logout process, displaying all the signed on services. The single logout screen displays the authentication status of each SP and whether any SPs can’t be logged out of (for example, if the SP is down or doesn’t support SLO). For non-Liferay DXP IdPs (Siteminder, ADFS, etc.) consult the vendor’s documentation on constructing IdP initiated SLO URLs.
The IdP sends a SAML LogoutRequest to the SP.
  • When Liferay DXP is configured as the IdP, the LogoutRequest is sent using either HTTP-Post, HTTP-Redirect, or SOAP binding. HTTP-Post binding is preferred but in its absence, the first available SLO endpoint with supported binding is selected.
  • When Liferay DXP is configured as the SP, supported bindings for LogoutRequest are HTTP-Post, HTTP-Redirect, or SOAP.
  • For other IdPs or SPs, please consult the vendor’s documentation.

The SLO Response from the SP

The SP delivers a LogoutResponse to the IdP. When Liferay DXP is configured as the SP, the LogoutResponse is delivered using either HTTP-Post, HTTP-Redirect, or direct response to SOAP request. HTTP-Post binding is preferred but in its absence, HTTP-Redirect is used. SOAP is only used to respond to the LogoutRequest over SOAP binding.
The IdP sends a SAML LogoutRequest to the second SP using either HTTP-Post, HTTP-Redirect, or SOAP binding.
The second SP then delivers the LogoutResponse to the IdP using HTTP-Post, HTTP-Redirect, or direct response to SOAP request. The process is repeated for all SPs the user is logged into. When Liferay DXP is the IdP, Liferay DXP logs the user out after the last SP has delivered its LogoutResponse or has timed out.

Service Provider Initiated SLO

saml-sp-initiated-slo.png
Figure 4: Service Provider Initiated SLO

The SLO Request to the SP

In SP initiated SLO, user’s browser requests logout directly to the SP. When Liferay DXP is configured as the SP, the SLO is initiated by requesting the logout URL
/c/portal/logout
For other SPs, consult the vendor’s documentation on initiating SLO.
A SAML LogoutRequest is sent to the Single Log Out service URL of the IdP.
  • If Liferay DXP serves as the SP, the LogoutRequest is sent to the IdP configured by the IdP Connection tab of the SAML provider (see the next article to set up the IdP Connection) and the SLO service URL defined in the SAML metadata. The request is sent using HTTP-POST or HTTP-Redirect binding.
  • When Liferay DXP is the IdP, if the user has logged on to other SPs the user is presented with a single logout screen with the status of each SP logout, flagging any that can’t be looged out of (some SPs might not support SLO or are currently down). If there are no other SPs to log out of, the SAML session terminates and the IdP destroys its session.

The SLO Response from the SP

If the user is logged in to additional SPs (beyond just the initiating SP), the IdP sends the SAML LogoutRequest to each one. When Liferay DXP is the IdP, the LogoutResponse is sent using either HTTP-Post, HTTP-Redirect, or SOAP binding.
Each SP delivers its LogoutResponse to the IdP. When Liferay DXP is the SP, the LogoutResponse is sent using either HTTP-Post, HTTP-Redirect or direct response to SOAP request.
After all additional SPs deliver their LogoutResponses to the IdP, the IdP destroys its SSO session. When Liferay DXP is the IdP, once the last SP has delivered its LogoutResponse or has timed out, the IdP destroys the Liferay DXP session, logging out the user.
Finally, the IdP sends a LogoutResponse to the SP that initiated SLO. The initiating SP terminates its SAML session and logs the user out.

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