The Shibboleth SP does not have an application API per se, but the SessionInitiator mechanism supports a simple redirect protocol capable of triggering, and influencing, the creation of authentication requests.

Initiator Protocol

This protocol supports a small set of query string parameters that correspond to identically named attributes that can be supplied either directly on a <SessionInitiator> element or as content settings on a per-resource basis.

When a query string parameter is used, it overrides any other source of the same setting/property.

Not all SessionInitiator handlers support all the possible parameters. In fact, most are specific to the SAML2 handler. Unsupported parameters are ignored.

entityID (URI)
- The IdP to request authentication from.

target (absolute URL)
- The URL to return the user to after authenticating. If unspecified, the homeURL attribute for the application is used.

acsIndex (string)
- The index value of the <md:AssertionConsumerService> element to instruct the IdP to use in returning an assertion to the SP.

forceAuthn (boolean) (defaults to false) (SAML2 only)
- Establish a value for the ForceAuthn attribute of the <samlp:AuthnRequest>. This asks for forced reauthentication by the IdP (bypassing SSO).

isPassive (boolean) (defaults to false) (SAML2 and SAMLDS only)
- Establish a value for the IsPassive attribute of the <samlp:AuthnRequest> or the IsPassive parameter of the DS redirect.

authnContextClassRef (URI) (SAML2 only)
- Requests that a particular authentication context class be used by the IdP. As of V2.5, this can be a whitespace-delimited list of classes to request.

authnContextComparison ("exact", "minimum", "maximum", "better") (defaults to "exact") (SAML2 only)
- Indicates the required relationship between a requested context class and the resulting form of authentication.

NameIDFormat (URI) (SAML2 only) (Version 2.3 and Above)
- If set, causes the authentication request to carry a saml:NameIDPolicy with a Format containing the provided value. If the receiving IdP can not fulfill this requirement it should return an error response.

SPNameQualifier (URI) (SAML2 only) (Version 2.3 and Above)
- If set, causes the authentication request to carry a saml:NameIDPolicy with an SPNameQualifier containing the provided value. If the receiving IdP can not fulfill this requirement it should return an error response.

discoveryPolicy (string) (SAMLDS only) (Version 2.5 and Above)
- Used as input to some discovery protocols that take parameters modifying discovery behavior. In the case of the type="SAMLDS"SessionInitiator, this is passed as a policy parameter value.
template (base64-encoded SAML <AuthnRequest> message) (SAML2 only) (Version 2.6 and Above)
- If supplied, the eventual SAML request is constructed based on the message supplied, apart from per-request information or settings supplied directly in the configuration or as parameters. Allows a message to be constructed externally with extensions or dynamic content, and then re-issued by the SP.

Examples

The redirection examples shown are illustrated by way of the HTTP Location header that would be returned to a client by an application. Refer to your programming environment's documentation for information on how to generate redirects and produce such a header. Note that you should always be sure to URL-encode any parameter values that you append.

The examples also assume that a SessionInitiator exists at the location "/Login", which is the usual default.

The most common scenario is to simply ask for a login while providing a resource to return the client to afterwards. Typically, this is the resource from which the redirect is generated.

Request a Session and Return to https://sp.example.org/resource.asp

Location: https://sp.example.org/Shibboleth.sso/Login?
  target=https%3A%2F%2Fsp.example.org%2Fresource.asp

Another common case is to specify the IdP to use. This is a simple way to implement user selection of an IdP from among a small set, for example clicking on a choice of logos. Not coincidentally, the SAMLDS handler is implemented by routing the result of the discovery process back to itself with the entityID parameter set.

Request a Session Using the IdP Named https://idp.example.org/idp/shibboleth

Location: https://sp.example.org/Shibboleth.sso/Login?
  target=https%3A%2F%2Fsp.example.org%2Fresource.asp&
  entityID=https%3A%2F%2Fidp.example.org%2Fidp%2Fshibboleth

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