ExternalAuthnConfiguration

Current File(s): conf/authn/external-authn-config.xml, conf/authn/authn.properties (V4.1+)
Format: Native Spring, Properties (V4.1+)

1 Overview
2 Enabling Module (V4.1+)
3 General Configuration
4 API
- 4.1 Inputs
- 4.2 Outputs
5 Reference

Overview

The authn/External login flow supports the use of an arbitrary external (to the IdP) authentication mechanism. Its basic function is to provide a non-WebFlow-based integration strategy for new authentication mechanisms. As a rule, using WebFlow is better and safer, but it does require writing Java code in most cases. This is usually true for external mechanisms also, but they can in some cases be implemented with JSP alone.

By default, the External flow is defined to lack support for advanced controls such as passive or forced authentication, but this can be changed if your integration supports these features.

This login handler usually requires additional code be written in order to trigger the external authentication system. If you're simply looking to authenticate based on the presence of REMOTE_USER, refer to the RemoteUser flow.

Once control is transferred to the external path, the IdP has no control over what happens, and it will implicitly trust any information passed back through the defined interface. If that information can be manipulated, security holes may result. The deployer takes full responsibility for the security of the overall exchange.

Enabling Module (V4.1+)

For V4.1+, configuring and using this feature requires that you first enable the "idp.authn.External" module if it isn't already enabled. Systems upgraded from older releases generally come pre-enabled due to the prior state of the configuration tree.

(Windows)
C:\opt\shibboleth-idp> bin\module.bat -t idp.authn.External || bin\module.bat -e idp.authn.External
 
(Other)
$ bin/module.sh -t idp.authn.External || bin/module.sh -e idp.authn.External

General Configuration

Use conf/authn/external-authn-config.xml to configure this flow.

The shibboleth.authn.External.externalAuthnPath bean defines the flow redirection path to the resource that's used to perform the external login, by default a context-relative location. It can be modified if needed, but must be a resource with access to the container session. Modify as needed to match the location of your external interface (see the documentation on flow redirects).

Most of the usual options are available via authn/authn.properties, and some more advanced cases will require defining/adjusting bean definitions in authn/external-authn-config.xml.

The idp.authn.External.externalAuthnPath property defines the flow redirection path to the resource that's used to perform the external login, by default a context-relative location. It can be modified if needed, but must be a resource with access to the container session. Modify as needed to match the location of your external interface (see the documentation on flow redirects).

You may also dynamically derive the path to use, typically so that it can vary based on aspects of the request, by defining a bean named shibboleth.authn.External.externalAuthnPathStrategy of type Function<ProfileRequestContext,String>.

The shibboleth.authn.External.ClassifiedMessageMap is a map of exception/error messages to classified error conditions. You can make use of this map either by modifying it to understand the error or exception messages returned by your external code, or by using the map as is and passing back the literal tokens in the map from your external code via the exception or error message interface.

API

The ExternalAuthentication class makes up the interface between the external code and the IdP. The general flow is:

Call ExternalAuthentication.startExternalAuthentication(HttpServletRequest), saving off the result as a key.
Do work as necessary (reading request details from the attributes below). Any redirects must preserve the key value returned in step 1 because it must be used to complete the login later.
Set request attributes to communicate the result of the login back.
Call ExternalAuthentication.finishExternalAuthentication(String, HttpServletRequest, HttpServletResponse). The first parameter is the key returned in step 1.

Example JSP implementations are below.

<%@ page pageEncoding="UTF-8" %>
<%@ page import="net.shibboleth.idp.authn.ExternalAuthentication" %>
<%@ page import="net.shibboleth.idp.authn.ExternalAuthenticationException" %>

<%
try {
    final String key = ExternalAuthentication.startExternalAuthentication(request);
    final String username = request.getRemoteUser();
    if (username != null) {
        request.setAttribute(ExternalAuthentication.PRINCIPAL_NAME_KEY, username);
    }
    ExternalAuthentication.finishExternalAuthentication(key, request, response);
     
} catch (final ExternalAuthenticationException e) {
    throw new ServletException("Error processing external authentication request", e);
}
%>

<%@ page pageEncoding="UTF-8" %>
<%@ page import="net.shibboleth.idp.authn.*" %>
<%@ page import="net.shibboleth.idp.attribute.*"%>
<%@ page import="net.shibboleth.idp.authn.principal.*"%>
<%@ page import="java.util.*"%>

<%
try {
    final String key = ExternalAuthentication.startExternalAuthentication(request);

    HashSet<Principal> principals=new HashSet<Principal>();

    principals.add(new UsernamePrincipal("bbarker"));

    //<DataConnector xsi:type="Subject" exportAttributes="mail eduPersonNickname" id="myId" />
    //<AttributeDefinition ... <InputDataConnector ref="myId" ...
    IdPAttribute attr=new IdPAttribute("eduPersonNickname");
    attr.setValues(Collections.singleton(new StringAttributeValue("Bob Barker")));
    principals.add(new IdPAttributePrincipal(attr));

    attr=new IdPAttribute("mail");
    attr.setValues(Collections.singleton(new StringAttributeValue("bbarker@example.org")));
    principals.add(new IdPAttributePrincipal(attr));

    request.setAttribute(ExternalAuthentication.SUBJECT_KEY,new Subject(false, principals, Collections.EMPTY_SET, Collections.EMPTY_SET));

    ExternalAuthentication.finishExternalAuthentication(key, request, response);

} catch (final ExternalAuthenticationException e) {
    throw new ServletException("Error processing external authentication request", e);
}
%>

Inputs

On first access to the external resource, the request attributes below will be set.

Name	Type	Function

Name	Type	Function
opensamlProfileRequestContext	ProfileRequestContext	Access to full request context tree
forceAuthn	Boolean	Whether the requester asked for re-authentication
isPassive	Boolean	Whether the requested asked for passive authentication
relyingParty	String	Name of the relying party requesting authentication
extended	Boolean	Whether this login flow has been invoked as an extension of another login flow

Outputs

Name	Type	Function

Name	Type	Function
principalName	String	Name of authenticated subject to use as the login result
principal	Principal	Java Principal object to use as the login result
subject	Subject	Java Subject object to use as the login result
authnError	String	Error message to return in place of a successful login
authnException	Exception	Explicit exception object to return in place of a successful login
authnInstant	Instant	Exact time of authentication to report back
authnAuthorities	Collection<String>	Ordered collection of URIs identifying upstream/proxied authenticating "authorities" used to authenticate the subject
attributes	Collection<IdPAttribute>	Collection of IdPAttribute objects to associate with the authenticated subject
doNotCache	Boolean	If true, prevents the result from being saved for future use for SSO
previousResult	Boolean	If true, the "new" AuthenticationResult is created with the "previousResult" flag set to true (mainly impacts auditing)

Only one "result" or error attribute should be set by the external code. Setting more than one has unspecified behavior. In most cases, the simple principalName should be returned on success, but you can return the more complex objects to pass back additional information such as public or private credentials or custom principal data.

Any IdPAttribute objects supplied will be processed by the AttributeFilter service as "inbound" data. If at least one value in the "authnAuthorities" attribute is supplied, it is set as the "issuer" of the attributes for the purposes of the filter evaluation.

Note that returning a Subject is often paired with setting the shibboleth.authn.External.addDefaultPrincipals bean (V4.0) or idp.authn.External.addDefaultPrincipals property (V4.1+) to false, to dynamically establish Principal(s) representing the authentication method used without having them overwritten.

For example, your External flow's supportedPrincipals property might be defined to include both password and multi-factor authentication Principals (meaning it supports both methods), but you can return the specific method used at runtime in the Subject. For SAML 2.0, this is typically done (programmatically) by using the net.shibboleth.idp.saml.authn.principal.AuthnContextClassRefPrincipal class with the appropriate value from the standard or a deployment. Other classes in that package address SAML 1.1 and unusual SAML 2.0 use cases. For the built-in constants defined by the standard, there are Java constants available via org.opensaml.saml.saml2.core.AuthnContext.

Reference

The beans defined, or expected to be defined, in authn/external-authn-config.xml follow:

Bean ID / Type	Default	Description

Bean ID / Type	Default	Description
shibboleth.authn.External.externalAuthnPath String	contextRelative:external.jsp	Spring Web Flow redirection expression for the protected resource
shibboleth.authn.External.externalAuthnPathStrategy Function<ProfileRequestContext,String>		Optional function that returns the redirection expression to use for the protected resource
shibboleth.authn.External.ClassifiedMessageMap Map<String,List<String>>	(see file)	A map between defined error/warning conditions and events and implementation-specific message fragments to map to them.
shibboleth.authn.External.resultCachingPredicate Predicate<ProfileRequestContext>		Optional bean that can be defined to control whether to preserve the authentication result in an IdP session
shibboleth.authn.External.addDefaultPrincipals Boolean	true	Whether to add the content of the `supportedPrincipals` property of the underlying flow descriptor to the resulting Subject
shibboleth.authn.External.matchExpression Pattern		Regular expression to match username against