Overview

The authn/WebAuthn login flow supports the Web Authentication API (WebAuthn) as part of the FIDO2 standard—enabling FIDO2 authentication. This allows public-key-based strong authentication of users. The plugin can operate as either a single-factor within a wider multi-factor authentication, as a single-factor where the username is supplied by the user (passwordless flow), or as a single-factor where the username is not supplied by the user (usernameless flows using passkeys).

Plugin Installation

Installation of Pre-release Plugin

In summary, use the plugin command that ships with the IdP to install the plugin from either a local file pre-downloaded from https://shibboleth.net/downloads/prerelease/ or directly via the pluggin URL.

Note: during the Alpha phase, the --noCheck option is required for successful installation.

Installation

C:>\opt\shibboleth-idp\bin\plugin.bat --noCheck -i https://shibboleth.net/downloads/prerelease/idp-plugin-webauthn-0.0.2.tar.gz

or

$ /opt/shibboleth-idp/bin/plugin.sh --noCheck -i https://shibboleth.net/downloads/prerelease/idp-plugin-webauthn-0.0.2.tar.gz

or

$ /opt/shibboleth-idp/bin/plugin.sh --noCheck -i <plugin.tar.gz>

If installing from a local file, you need to ensure the GPG detached signature (e.g. the .asc file) is placed alongside the main plugin archive on disk.

If it has not been seen before, you will be asked to accept the key signing that signed the module into the trust store for this plugin. See PluginTrust for more information on how to ensure the contents of the plugin have not been modified.

Listing Installed Plugins

$ /opt/shibboleth-idp/bin/plugin.sh -l

or

C:>\opt\shibboleth-idp\bin\plugin.bat -l

Enabling the Module

For a detailed guide on configuring modules, see the ModuleConfiguration topic. Once the plugin has been installed, its module should be enabled automatically for you:

Check Module Is Enabled

/%{idp.home}/bin$ ./module.sh -l

...
Module: idp.authn.WebAuthn [ENABLED]

However, if you need to enable it you can using the module command:

Enable the module

/%{idp.home}/bin$ ./module.sh -e idp.authn.WebAuthn

Either manual or automatic module enablement will copy across the following configuration files from the jar:

Configuration files

Authentication Flow

Overview of Configuration Steps

• Configure the plugin

  • Add the relyingPartyId to conf/authn/webauthn.properties

  • Add the relyingPartyName to conf/authn/webauthn.properties

• Decide how the flow should be used.

• Configure the MFA flow to use the WebAuthn authentication method

  • Add the MFA flow to the idp.authn.flows property in conf/authn/authn.properties.

• Think about which Authentication Context Class (Supported Principals) the flow should expose

• Register a FIDO2 credential through the registration admin flow

• Show your administrator how to remove user credentials

Configuration of the WebAuthn Relying Party

The IdP acts as a WebAuthn Relying Party when initiating the Web Authentication API to register and authenticate users. The identity of the Relying Party (IdP) must be configured in conf/authn/webauthn.properties.

• The relyingPartyId: A valid domain string. Set to the IdP’s origin’s effective domain. FIDO2 credentials are scoped to, and can only be used for, a relying party. It does not include a scheme or port (as a normal origin would). Credentials are scoped to the Relying Party ID.

  • Note, ‘localhost’ can be used for testing.

• The relyingPartyName: a human-palatable identifier for the relying party. Used for display purposes.

• Optional allowPortOrigin: If true, any port is allowed for the given origin.

• Optional allowOriginSubdomain: If true, any subdomain (of any depth) is allowed for the given origin.

• Optional allowOrigins: Comma-separated set of origins to allow in responses from an authenticator for this Relying Party. If not set, the Relying Party ID is used (assuming the https scheme and the default port). Note, unlike the Relying Party ID, this includes the scheme and port.

# The IdP's origin
idp.authn.webauthn.relyingPartyId = localhost
idp.authn.webauthn.relyingPartyName = My IdP Name
# Allow any port of 'localhost'
idp.authn.webauthn.allowOriginPort = true
# Do not allow any subdomain of 'localhost'
idp.authn.webauthn.allowOriginSubdomain = false

Authentication flows

The WebAuthn flow is capable of running as either a second single-factor authentication (similar to U2F, but using the WebAuthn APIs) or as a first and only factor of authentication which could still satisfy multi-factor requirements (device bound passkeys such as those found on a hardware security key, for example incorporating two factors; something the user has and something the user is. However, multi-device synched passkeys are not, technically, something you have—although they may still provide adequate multi-factor authentication assurances in certain circumstances). When acting in a first-factor authentication mode, the flow can be configured as either a usernameless (passkey) flow or passwordless flow: this is toggled using the idp.authn.webauthn.usernameless.enabled property.

Usernameless (Passkey) flow

A usernameless flow does not require the user to enter their username during authentication. To support a usernameless flow, the authenticator must allow Discoverable Credentials (previously known as a Resident Key and now referred to as a passkey) where the private key and associated metadata is stored on the authenticator (FIDO2 compatible authenticators should work). This is important, as the IdP, without a known username, will not be able to preselect a user and credential to use; this must come instead from the user selecting the correct credential—suitable for the IdPs origin—from the authenticator itself.

During authentication, the authenticator is required to:

• test the user is present by using some form of authorization gesture (for example, by touching the authenticator or clicking on a key to use), and

• verify the user’s identity by some form of local authorization (for example, using a pin code or biometric recognition).

Passwordless flow

Collecting the username is the initial step in a passwordless flow, and therefore, it does not require storing credentials on the authenticator. Instead, for example, the credential can be encrypted and stored on the server (possibly in the credential ID sent to the server during registration and returned by the IdP during authentication).

During authentication, the authenticator is required to:

• test the user is present by using some form of authorization gesture (for example, by touching the authenticator or clicking on a key to use), and

• verify the user’s identity by some form of local authorization (for example, using a pin code or biometric recognition), and

• test the credential requested by the IdP and used by the authenticator is allowed (has been registered with the IdP).

Second factor authentication (2FA) flow

The WebAuthn flow will operate in second-factor mode automatically only if three conditions are met. First, the property idp.authn.webauthn.2fa.enabled must be set to true. Second, a previous authentication factor must have produced an Authentication Result from the MFA context. Finally, a principal name must be found through a lookup strategy by default from the C14N context or the Session Context using the CanonicalUsernameLookupStrategy. If these conditions are not met, authentication will revert to either a passwordless or usernameless flow (depending on which is enabled).

The acceptable previous factors can be controlled by listing (comma-separated) authentication flows in the property idp.authn.webauthn.2fa.allowedPreviousFactors. The default is authn/Password.

If enabled, and you want to completely bypass the existing logic such that the WebAuthn flow for 2FA is always used, you can set the property idp.authn.webauthn.2fa.forceSecondFactorFlow to true.

When acting as a 2nd factor of authentication, the username is gathered from the principal name as a result of the first factor by lookup strategy and any credentials registered to that username are retrieved. During authentication, the authenticator is then required to:

• test the user is present by using some form of authorization gesture (for example, by touching the authenticator or clicking on a key to use), and

• test the credential used is allowed (has been registered with the IdP).

This mode must be used within an appropriate MFA flow, where authn/WebAuthn is used as the second factor.

Configuration of the MFA flow

Before you start, make sure to enable the MFA login module and configure the flow in conf/authn/authn.properties. It should be possible to run the WebAuthn plugin as a standalone authentication method for the IdP. However, it is designed to work within a multi-factor authentication (MFA) flow. Even when used alone to provide single-factor authentication, this design allows for greater flexibility when configuring authentication routes. For example, if no credentials are available for WebAuthn authentication, it can fall back to using a password.

WebAuthn as the sole factor of authentication

In its simplest form, you can set up the WebAuthn plugin to be the only means of authentication in either usernameless or passwordless modes.

Note, that configuring only WebAuthn authentication will also require a FIDO2 credential to access the registration flow. Hence, unless you have another mechanism of seeding the registration of credentials within the credential repository, the user will not be able to access the registration page: please see the final example for a possible solution to this.

<util:map id="shibboleth.authn.MFA.TransitionMap">    
        <entry key="">
          <bean parent="shibboleth.authn.MFA.Transition" p:nextFlow="authn/WebAuthn" />
      </entry>
  </util:map>  

WebAuthn as a second factor of authentication

As described in the second-factor authentication section, the WebAuthn flow can be used as a second factor of authentication where the user only needs to demonstrate possession of a registered credential (typically via a user gesture such as pressing a physical or virtual button). A simple MFA configuration which runs the Password flow before determining if the WebAuthn flow should run is shown below:

<util:map id="shibboleth.authn.MFA.TransitionMap">    
        <entry key="">
          <bean parent="shibboleth.authn.MFA.Transition" p:nextFlow="authn/Password" />
      </entry>
      <entry key="authn/Password">
          <bean parent="shibboleth.authn.MFA.Transition" p:nextFlowStrategy-ref="checkSecondFactor" />
      </entry>
  </util:map>   
    
  <!-- If password flow is not enough, use WebAuthn flow as a 2nd factor. Although that will not work if no credentials -->
  <bean id="checkSecondFactor" parent="shibboleth.ContextFunctions.Scripted" factory-method="inlineScript">
      <constructor-arg>
          <value>
          <![CDATA[
              nextFlow = "authn/WebAuthn";
              // Check if second factor is necessary for request to be satisfied.
              authCtx = input.getSubcontext("net.shibboleth.idp.authn.context.AuthenticationContext");
              mfaCtx = authCtx.getSubcontext("net.shibboleth.idp.authn.context.MultiFactorAuthenticationContext");
              if (mfaCtx.isAcceptable()) {
                  nextFlow = null;
              }
              nextFlow;   // pass control to second factor or end with the first
          ]]>
          </value>
      </constructor-arg>
  </bean>

WebAuthn as the sole factor but with password fallback for registration

The following MFA configuration establishes the WebAuthn plugin as a sole, single-factor, authentication method. However, it also permits the auth/Password flow to be used if the user is in a WebAuthn Registration flow and has not yet enrolled any FIDO2 credentials. This allows users to register their first FIDO2 credential by authenticating against their username and password (and possibly a different second-factor). After the first credential has been enrolled, there is no fallback option, and subsequent registration attempts will require a FIDO2 credential.

<util:map id="shibboleth.authn.MFA.TransitionMap">    
     <entry key="">
        <bean parent="shibboleth.authn.MFA.Transition" p:nextFlowStrategy-ref="checkPasswordOrWebAuthn" />
    </entry>
</util:map>

<!-- Use the webauthn flow unless a registration context exists and the user does not have any FIDO2 credentials registered,
   then use a password flow.-->
 <bean id="checkPasswordOrWebAuthn" parent="shibboleth.ContextFunctions.Scripted" factory-method="inlineScript">
    <constructor-arg>
        <value>
        <![CDATA[
            nextFlow = "authn/WebAuthn"
            // Check if we can use a WebAuthn flow, or if the user has no credentials available to them use a password flow
            webauthnRegCtx = input.getSubcontext("net.shibboleth.idp.plugin.authn.webauthn.context.WebAuthnRegistrationContext");
            if (webauthnRegCtx != null){
                if (!webauthnRegCtx.isWebAuthnAvailable()){
                    nextFlow = "authn/Password"
                }
            }       
            nextFlow;   // pass control to WebAuthnFlow
        ]]>
        </value>
    </constructor-arg>
</bean>

Signalling custom events when the user has no registered credentials

In case the user has not registered any FIDO2 credentials, there are two ways to signal a custom event to the IdP. The first signal can be emitted just after collecting the username for the passwordless or 2fa flows. The second signal can be emitted after the authenticator has sent the attestation (authentication) response back to the IdP—this is the only signal you can expect from the usernameless (passkey) flow since there is no username collection step.

For the passwordless and second factor flows, setting idp.authn.webauthn.passwordless.signalEventOnNoCredentials to true will signal a custom event ID (described by the property idp.authn.webauthn.passwordless.noCredentialsEventId) If the user (identified by the username entered in the username input step) has no registered FIDO2 credentials. This will signal a custom event immediately after username collection, ending the flow. To have return controlled to the MFA orchestration layer, the event must be described to the system in the conf/authn/authn-events-flow.xml in the usual way (see the example below).

For all flows, but specifically for a usernameless (passkey) flow, setting idp.authn.webauthn.signalEventOnNoCredentialsRegisteredForUserHandle to true will signal a custom eventID (described by the property idp.authn.webauthn.userHandleNoRegisteredCredentialsEventId) if the user, identified by the userHandle (user.id) in the authenticator's attestation response, does not belong to a known user with at least one registered FIDO2 credential. The event is signalled just before the attestation (authentication) response is validated. Again, the event must be described to the system in the conf/authn/authn-events-flow.xml in the usual way if it is to be used as a transition in the MFA flow (see the example below).

<flow xmlns="http://www.springframework.org/schema/webflow"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://www.springframework.org/schema/webflow http://www.springframework.org/schema/webflow/spring-webflow.xsd"
      abstract="true">

    <!-- ADVANCED USE ONLY -->
    
    <!--
    You can ignore this file unless you are creating your own custom login subflows that want to
    report custom events in response to unusual error or warning conditions.
    -->

    <!-- Custom error events to reflect back from user-supplied login subflows. -->

    <end-state id="NoRegisteredWebAuthnCredentials" />
    <end-state id="NoCredentialsRegisteredForUserHandle" />

    <global-transitions>
        <transition on="NoCredentialsRegisteredForUserHandle" to="NoCredentialsRegisteredForUserHandle" />
        <transition on="NoRegisteredWebAuthnCredentials" to="NoRegisteredWebAuthnCredentials" />
        <transition on="#{!'proceed'.equals(currentEvent.id)}" to="InvalidEvent" />
    </global-transitions>

</flow>

<util:map id="shibboleth.authn.MFA.TransitionMap">
    
        <entry key="">
            <bean parent="shibboleth.authn.MFA.Transition" p:nextFlow="authn/WebAuthn" />            
        </entry> 
        
         <entry key="authn/WebAuthn">
            <bean parent="shibboleth.authn.MFA.Transition">
                <property name="nextFlowStrategyMap">
                    <map>          
                        <entry key="NoRegisteredWebAuthnCredentials" value="SomeOtherFlow" />
                        <entry key="NoCredentialsRegisteredForUserHandle" value="SomeOtherFlow" />
                    </map>
                </property>
            </bean>
        </entry> 

    </util:map>

WebAuthn as the sole factor using custom events to drive a fallback for registration and authentication

Some MFA configurations discussed so far allow a different authentication method to run as a fallback if the user has no registered FIDO2 credentials. This requires the registration step to provide its own username collection page so a decision can be made about which flow to follow when the user has not registered any credentials. This only affects registration, if a user performs authentication without first registering a FIDO2 credential, the authentication flow will ultimately fail. This is probably a good thing, however, for flexibility it is possible to disable username collection on the registration flow and delegate ‘NoCredentials’ signalling to the authentication flow using custom events.

To disable username collection on the registration flow, set the idp.authn.webauthn.registration.collectUsername property to false. Then, configure the MFA flow to trigger a different authentication flow if the user has no credentials—following the examples in the custom events topic. It is worth noting this will affect registration and standard authentication. That is, any user without credentials will end up signalling those custom events, and, if the MFA flow is set up with a fallback flow, they will authenticate using that fallback. For registration you can of course require that the fallback method (all methods really) was of a particular quality by setting the default authentication methods property idp.authn.webauthn.admin.registration.defaultAuthenticationMethods to require MFA (or whatever you want). Similarly, if the Service Provider has requested MFA in their request, the authentication fallback for a standard authentication also needs to support it.

WebAuthn as the sole factor using custom events to drive a different two-factor fallback for authentication and registration

Enabling event signalling when a user does not yet have a registered FIDO2 credential (see the previous section), allows us to configure a different type of two-factor authentication fallback. For example, the following will first run the WebAuthn flow which will fail if the user has no existing registered credentials, it then proceeds to the auth/Password flow and, if required (e.g, requested by the SP), to the authn/DuoOIDC flow. If either registration or admin flows are configured to require MFA (by setting their default authentication methods), they will also fall back to authn/Password and authn/DuoOIDC. Once users have registered their first key, they will proceed only to use the WebAuthn plugin for authentication.

<util:map id="shibboleth.authn.MFA.TransitionMap">
    
        <entry key="">
            <bean parent="shibboleth.authn.MFA.Transition" p:nextFlowStrategy-ref="checkPasswordOrWebAuthnForRegistration" />            
        </entry>       
        
         <entry key="authn/WebAuthn">
            <bean parent="shibboleth.authn.MFA.Transition">
                <property name="nextFlowStrategyMap">
                    <map>          
                        <entry key="NoRegisteredWebAuthnCredentials" value="authn/Password" />
                        <entry key="NoCredentialsRegisteredForUserHandle" value="authn/Password" />
                    </map>
                </property>
            </bean>
        </entry>         
        <entry key="authn/Password">
            <bean parent="shibboleth.authn.MFA.Transition" p:nextFlow="authn/WebAuthn" />            
        </entry>
    </util:map>
    
    <!-- If the MFA context is not acceptable from the first factor, run the DuoOIDC flow -->
    <bean id="checkSecondFactor" parent="shibboleth.ContextFunctions.Scripted" factory-method="inlineScript">
        <constructor-arg>
            <value>
            <![CDATA[
                nextFlow = "authn/DuoOIDC";
                // Check if second factor is necessary for request to be satisfied.
                authCtx = input.getSubcontext("net.shibboleth.idp.authn.context.AuthenticationContext");
                mfaCtx = authCtx.getSubcontext("net.shibboleth.idp.authn.context.MultiFactorAuthenticationContext");
                if (mfaCtx.isAcceptable()) {
                    nextFlow = null;
                }
                nextFlow;   // pass control to second factor or end with the first
            ]]>
            </value>
        </constructor-arg>
    </bean>

Authentication Context Classes (Supported Principals)

As with all authentication flows, the WebAuthn plugin exposes a collection of supportedPrincipalscompatible with the type of authentication mechanism used. By default, the idp.authn.webauthn.supportedPrincipals property contains placeholder examples for what these could be.

The set you specify for the flow is entirely up to you based on the type of authentication flow you have configured, and what authentication assurances you want. For example, when used as a second-factor in 2FA mode, it seems feasible to signal MFA from the WebAuthn plugin. On the other hand, using the plugin as a sole-factor, in either passwordless or usernameless modes might not be sufficient to signal MFA unless you knew the credential was device-bound (which you can not currently determine from the plugin). Even if the typical passkey process combines ‘something you are’ (biometrics) or ‘something you know’ (pin) with ‘something you have’ (an authenticator), if the credential is synchronised (as common with passkey providers such as iCloud Keychain and Google Password Manager) it is arguable the authenticator isn’t ‘something you have’. Either way, it is up to you to decide how best to handle this.

Credential Repository

The plugin's critical component is the credential repository which stores and loads credential registrations. The default credential repository utilizes the Shibboleth Storage Service, but it's also possible to utilize other repository implementations by extending the WebAuthnCredentialRepository interface. The default repository uses the configured shibboleth.StorageService, although it is possible to override this by specifying a different bean in the idp.authn.webauthn.StorageService property.

In theory, any implementation of a storage service should be compatible, but it's important to consider its capabilities before using it. For example, for testing, you can use client-storage by referencing (in that property) the bean shibboleth.ClientSessionStorageService. But that will store your credential registrations in the browser and is not portable across browsers—although the credentials will survive an IdP restart so it might be useful during initial testing.

In production, you might want to use a JDBC storage option. The following example shows how this might work.

CREATE SCHEMA IF NOT EXISTS `webauthn`;

CREATE TABLE webauthn.StorageRecords (
  context varchar(255) NOT NULL,
  id varchar(255) NOT NULL,
  expires bigint DEFAULT NULL,
  value text NOT NULL,
  version bigint NOT NULL,
  PRIMARY KEY (context, id)
);

    <bean id="shibboleth.JDBCDataSource" class="org.mariadb.jdbc.MariaDbDataSource">
        <property name="url" value="jdbc:mariadb://localhost:3306/webauthn" />
        <property name="user" value="<user>" />
        <property name="password" value="<password>" />
    </bean>
    
    <bean id="shibboleth.WebAuthnStorageService" parent="shibboleth.JDBCStorageService"
        p:cleanupInterval="%{idp.storage.cleanupInterval:PT10M}" 
        p:dataSource-ref="shibboleth.JDBCDataSource"/>

Credential Registration Flow

The plugin comes with an administration flow for registering and managing FIDO2 credentials. The inbuilt flow represents the minimum viable product for implementing such a feature. In the future other plugins may provide this functionality.

The registration flow can be accessed by navigating to:

http[s]://hostname/idp/profile/admin/webauthn-registration

The registration flow collects the username as a first step so it can look up any registered credentials before passing control to the authentication system. This information can be accessed in the MFA configuration using the isWebAuthnAvailable() method on the WebAuthnRegistrationContext, to decide which flow to use. The example MFA Flow With Password Fallback is a suitable initial setup that allows users to register their first credentials upon inputting their username and password; other combinations are possible.

Overview of Configuration Steps

Other than following step 1, you do not need to change any of the default registration options to register and use a FIDO2 credential with the IdP successfully. If you do want more control over the process, there are a few options available:

1. (Required) Configure a suitable access control policy.

2. (Optional) Configure how user account details are passed to the WebAuthn API and authenticator.

3. (Optional) Decide what type of authenticator you want to support.

4. (Optional) Decide if you want to require only ‘trusted’ (from FIDO Alliance Metadata) authenticators to be registered

AccessPolicy Configuration

The user and client accessing the registration flow are subject to an AccessControlConfiguration set by the property idp.authn.webauthn.admin.registration.accessPolicy. The default policy, AccessByCurrentUser, is not defined in the IdP's access control configuration and needs to be added for the flow to load: add it to the map in conf/access-control.xml like so:

...
    <entry key="AccessByCurrentUser">
        <bean parent="shibboleth.PredicateAccessControl">
            <constructor-arg>
                <bean id="AccessByCurrentUserPredicate" 
                    class="net.shibboleth.idp.plugin.authn.webauthn.admin.impl.AllowCurrentUserAccessPredicate">
                </bean>
            </constructor-arg>
        </bean>
    </entry>
...

This policy is essential if you plan on creating an MFA flow (such as MFA Flow With Password Bypass) which provides another authentication method if the user has no registered credentials: either using isWebAuthnAvailable() or when signalling a custom event.

The AccessByCurrentUser policy checks the username found in the registration context—collected by the username view when the user first enters the registration flow—is the same as the principal name (identity) of the user that authenticated. This is important, if we imagine a scenario where a nefarious user wanted to ‘change' or possibly 'downgrade’ a user’s authenticate method from WebAuthn to, say, username and password (or whatever else was configured as a ‘backup’), all they would need to do is enter a non-existent username into the username collection step of the registration page and then have the MFA flow direct them to a different flow (because they do not have any registered credentials) where, for example, they can proceed to try different usernames and passwords for authentication. Importantly, the registration flow uses the principal name of the authenticated user to register credentials against.

The AccessByCurrentUser policy safeguards by ensuring that the username initially entered into the registration page—for which the credentials are retrieved, and any flow decision is based—matches the authenticating user's principal name. If they do not match, access to the registration page is denied. This measure prevents a user from switching usernames between the registration and authentication flows.

However, there are some caveats to consider. The principal name that results from authentication is determined by the Authentication flow, the SubjectCanonicalization flow, and possibly any transformations that have been applied to the username. It is, therefore, entirely possible (although probably not common) that the user who entered the registration flow is the same as the user who authenticated, but their username and principal name do not match. Generally, if this is the case, a different comparison predicate would need to be created and plugged into the AccessByCurrentUser policy: see the example below.

<entry key="AccessByCurrentUser">
    <bean parent="shibboleth.PredicateAccessControl">
        <constructor-arg>
            <bean id="AccessByCurrentUserPredicate" 
                class="net.shibboleth.idp.plugin.authn.webauthn.admin.impl.AllowCurrentUserAccessPredicate">
                <property name="comparisonPredicate">
                    <bean id="StringMatchComparisonPredicate"
                        class="net.shibboleth.idp.plugin.authn.webauthn.admin.impl.AllowCurrentUserAccessPredicate$DefaultCurrentUserComparisonPredicate">
                          <property name="comparisonPredicate">
                              <bean ...
                              </bean>
                          </property>
                      </bean>                        
                </property>
            </bean>
        </constructor-arg>
    </bean>
</entry>

If the applied transformations are simple enough and the simple-subject-c14n (or similar) flow is used to expose the UsernamePrincipal as the principal name, it may be feasible to match the username entered in the registration process by adjusting the following properties.

1. idp.authn.webauthn.registration.username.uppercase : upper case the username?

2. idp.authn.webauthn.registration.username.lowercase : lowercase the username?

3. idp.authn.webauthn.registration.username.trim : trim the username?

And supplying any transformations by defining the bean, shibboleth.authn.webauthn.registration.UsernameTransformations.

Note, if you do this and you are using the passwordless authentication mode, you will need to supply the same transformation settings to the authentication flow, otherwise, it will not match with the username used to register the credential.

1. idp.authn.webauthn.passwordless.username.uppercase : upper case the username?

2. idp.authn.webauthn.passwordless.username.lowercase : lower case the username?

3. idp.authn.webauthn.passwordless.username.trim : trim the username?

And supplying any transformations by defining the bean, shibboleth.authn.webauthn.passwordless.UsernameTransformations.

User Identity for Credential Generation

During registration, the IdP will pass user account details to the WebAuthn API. Some of this information is used to improve the user experience whilst creating credentials, and some are used by the authenticator to bind credentials to user accounts at the IdP.

The generation of this information is described in the following sections.

User ID (UserHandle) Population

The user ID (user.id) should be the primary key of the user account within the IdP, it must not exceed 64 bytes in length, and It should not include personally identifiable information. The ID should not change and is used by the authenticator to bind a credential to a user during registration with the IdP. In an authentication response, it is returned as the user handle.

In this context, the credential is registered against the IdP and so the user ID of the credential will be the same no matter who the requesting, upstream, service provider is—an authenticator will only store one credential for the IdP per user ID.

By default, the user ID is generated at runtime using a random byte sequence of 64 bytes. However, you may prefer to pull this value from the attribute resolver. This is supported by changing the following properties in conf/authn/webauthn.properties:

1. change the property idp.authn.webauthn.registration.userid.strategy to reference the bean shibboleth.authn.webauthn.AttributeContextUserIdLookupStrategy.

2. ensure the attribute resolver is enabled after authentication, idp.authn.webauthn.admin.registration.resolveIdentityAttributes=true.

3. decide which attribute from the resolver context to use using idp.authn.webauthn.registration.userid.attributeId.

   1. Note, the AttributeContextUserIdLookupStrategy requires the attribute to be a single StringAttributeValue converted to a byte array assuming a UTF-8 character set.

Complete control over the strategy is possible by defining your own strategy of type Function<ProfileRequestContext, byte[]>.

User Name Population

The user name (user.name) is a human-palatable identifier for a user’s account a credential is associated with. During authentication, it will become the UsernamePrincipal of the subject. It may be truncated by the authenticator to 64 bytes.

By default, this is taken from the principal name of the user who authenticated (contained in the SubjectContext). This can be changed by creating a bean in conf/authn/webauthn-config.xml referenced by the idp.authn.webauthn.registration.username.strategy in conf/authn/webauthn.properties.

User Display Name Population

The user display name (user.displayName) is a human-palatable name for the user’s account. It is only intended for display to the user during registration. It is not used during authentication.

By default, the user display name is taken from the principal name in the SubjectContext. That is, the canonical principal name of the subject that authenticated to the registration endpoint. However, you may prefer to pull this value from the attribute resolver. This is supported by changing the following properties in conf/authn/webauthn.properties:

1. change the property idp.authn.webauthn.registration.displayname.strategy to reference the bean shibboleth.authn.webauthn.AttributeContextDisplayNameLookupStrategy.

2. ensure the attribute resolver is enabled after authentication, idp.authn.webauthn.admin.registration.resolveIdentityAttributes=true.

3. decide which attribute from the resolver context to use using idp.authn.webauthn.registration.displayname.attributeId.

Complete control over the strategy is possible by defining your own strategy of type Function<ProfileRequestContext, String>.

Credential Generation Options

Discoverable Credentials (Passkeys)

A Discoverable Credential, formally a Resident Key, stores the private key and associated metadata on the authenticator. This allows usernameless flows and is strictly what is required for a FIDO2 credential to be a ‘passkey’. The alternative allows the private key to be stored, in a protected format, at the relying party (for example, packaged inside the credential ID). Noting that some security keys have limited space for Discoverable Credentials.

Technically, a Discoverable Credential can either be synchronised via some sync fabric (a multi-device or synched passkey e.g, cloud-synched via iCloud Keychain) or bound to the device (single-device or device-bound passkey e.g, a security key). Note that currently there is no way in the plugin to set or detect the different types, the W3C work on this is still a working draft.

During the registration of a FIDO2 credential, you can explicitly configure the ResidentKeyRequirement by setting the idp.authn.webauthn.registration.residentKey property. The possible values, set in conf/authn/webauthn.properties, are listed below:

If you ‘preferred’ Discoverable Credentials during registration but require them for authentication, you may end up in a situation where the user registers a credential they can not later use.

Authenticator Attachment Options

Authenticator attachment modality specifies the mechanism by which a client can communicate with an authenticator. For example, can the authenticator be removed and ‘roam’ across platforms like a security key, or is the authenticator internal to the device and attached to the given platform like a Trusted Platform Module.

This distinction between roaming and platform attachments can be confusing when a platform authenticator can also be used in a roaming context. The most common example of this is that of a mobile device authenticator: when authenticating on the device itself it acts as a platform authenticator, but when authenticating another client via cross-device authentication (QR code and Bluetooth) it acts as a roaming authenticator.

During the registration of a FIDO2 credential, you can explicitly configure the AuthenticatorAttachment by setting the idp.authn.webauthn.registration.authenticatorAttachment property. The possible values, set in conf/authn/webauthn.properties, are listed below:

Attestation Conveyance

Attestation allows the IdP (acting as a WebAutun RP) to verify the provenance of the authenticator used when registering a FIDO2 credential. This is provided in the form of an attestation statement. Attestation is optional as it can provide a poor user experience (the user must consent to the release of the attestation statement during registration), has an unclear meaning if the credential is synchronised around multiple devices (what created it might not be the same as what eventually uses it), and is a possible privacy concern (adds another data point for fingerprinting).

During registration of a FIDO2 credential, you can explicitly configure the AttestationConveyencePreference by setting the idp.authn.webauthn.registration.attestationConveyancePreference property. The possible values, set in conf/authn/webauthn.properties, are listed below:

Noting, if you want to use the basic support for only allowing credentials to be registered from ‘trusted’ authenticators that are contained within the FIDO metadata feed, you’d typically need to enable ‘direct’ attestation.

User Verification

User verification requires an authenticator to authorise a user to create or use credentials. Typically this involves some kind of authorization guester such as fingerprint recognition, face recognition, or a pin.

During the registration of a FIDO2 credential, you can explicitly configure the AttestationConveyencePreference by setting the idp.authn.webauthn.registration.userVerification property. The possible values, set in conf/authn/webauthn.properties, are listed below:

Note that if user verification is required during registration, you may exclude authenticators that are usable in second-factor scenarios (which don’t require a user-verification capable authenticator).

Other Registration Options

The following additional registration options can be set in conf/authn/webauthn.properties.

FIDO Metadata Service Support

The plugin supports Authenticator Metadata obtained from the FIDO metadata service (FIDO Alliance Metadata Service - FIDO Alliance). When enabled, this provides the following additional features during registration:

1. Validation of authenticator attestations. Specifically, only allowing credentials to be registered from ‘trusted’ authenticators that are contained within the metadata.

2. Enhancing the registration interface to display information about the user’s Authenticator: the device description and organisational icon.

Globally enabling the feature requires setting the idp.authn.webauthn.metadata.enabled property. Then, you have a choice of either downloading the metadata blob from the FIDO alliance Metadata Service URL (currently https://mds3.fidoalliance.org/), or, downloading the blob yourself, storing it locally, and pointing to the local file. The metadata does not change very often, but the FIDO guidelines suggest obtaining a new copy every month. Currently, this would require a restart of the IdP to pick up the new metadata.

For an authenticator to transmit an attestation statement to the IdP, which includes details about itself for matching with metadata entries, the IdP must initiate the registration request with an AttestationConveyancePreference. This can be set using the idp.authn.webauthn.registration.attestationConveyancePreference property. This defaults to ‘none’ (do not send an attestation statement), however a value of ‘direct’ or ‘enterprise’ would be needed to ensure this feature operated reliably (see the specification for more information). Please note that during registration, users must consent to sending the attestation statement to the IdP, and knowing the authenticators users are using may raise privacy concerns for the IdP.

Downloading the metadata blob from the FIDO metadata service URL

If you want to download metadata from the FIDO Alliance’s centralised repository when the IdP starts, you must specify a cache file (ending .bin) using the property idp.authn.webauthn.metadata.cacheFile, and the URL to fetch the metadata from using the property idp.authn.webauthn.metadata.metadataBlobUrl (by default this is https://mds3.fidoalliance.org/, although that can change, see https://fidoalliance.org/metadata/).

Downloading the metadata blob manually

As an alternative to downloading the metadata blob from a URL on startup of the IdP, you can choose to manage the metadata blob yourself. Download the blob JWT from the FIDO metadata service https://fidoalliance.org/metadata/ (currently, https://mds3.fidoalliance.org/) and load it using the property idp.authn.webauthn.metadata.metadataBlobFile.

Metadata Blob Trust Validation

To verify the integrity and authenticity of the metadata blob, you must download the trust root certificate listed at https://fidoalliance.org/metadata/ and load it using the property idp.authn.webauthn.metadata.trustRootFile. This is important because the metadata blob provides the trust roots for Authenticator Attestations and hence we need to first bootstrap trust for the metadata itself (as you would with SAML Metadata).

Revocation Checking

According to the FIDO MDS Specification, the revocation status of the certificates used in the metadata blob’s digital signature MUST be checked for the metadata to load. If you enable metadata support but do not enable revocation checking, the IdP will fail to start. There are two ways to enable this:

1. Download and manage the CRLs present in the Metadata blob certificate path manually, and point to them using the idp.authn.webauthn.metadata.crls property.

   1. For the current signing certificate, these are at http://crl.globalsign.com/root-r3.crl and http://crl.globalsign.com/gs/gsextendvalsha2g3r3.crl. You’d need to keep these up to date to a) prevent them from expiring, and b) perform meaningful revocation checks.

2. Comment out the idp.authn.webauthn.metadata.crls property and enable automated CRL checking from an online distribution point via the system property com.sun.security.enableCRLDP (as described in the CertPathDocs).

   1. This will enable CRL distribution points for the Sun PKIX engine across the IdP. So be careful this is what you want to do before enabling it.

Administrative Credential Management Flow

In addition to user management of their credentials, there is an admin flow for administrators to manage other users' credentials. Specifically, to search for and remove a user's registered credential from the system.

The management flow can be accessed by navigating to:

http[s]://hostname/idp/profile/admin/webauthn-management

As with the registration flow, the management flow will use whichever authentication method is enabled. Importantly, the client and user accessing the management function are subject to an AccessControlConfiguration set by the property idp.authn.webauthn.admin.management.accessPolicy; by default, this is the AccessByAdminpolicy. Given the purpose of this flow, it is important to ensure a suitably restrictive access policy is set. Furthermore, it is essential to ensure that an appropriate authentication method is executed, even if a fallback has been configured for administrators lacking FIDO2 credentials. This is controlled by the idp.authn.webauthn.admin.management.defaultAuthenticationMethods property, which defaults to saml2/<http://example.org/ac/classes/mfa>. This default setting is intentional, careful consideration should be given if you change this setting.

The process is straightforward: initially, you search for a user by their User Name to display their registered credentials. Subsequently, you have the option to delete one or more of these credentials before completing the process.

Debugging Registration and Authentication Requests

If you want to easily see and debug both the registration ceremony (PublicKeyCredentialCreationOptions) and authentication ceremony (PublicKeyCredentialRequestOptions), you can set the idp.authn.webauthn.ui.debug property to true in conf/authn/webauthn.properties. The requests should appear on the authentication and registration views in a drop-down box.

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