Generate SAML 2 AuthnRequest by using OpenSAML 3

Hi,

I will start series of posts on SAML 2 about how to generate messages, parsing them and validating them.

First of all, to dig into the subject I really recommend to read the saml technical overview. It has everything needed to understand SAML and it is well written.

In this post I will show how to generate an AuthN request using Java and we will validate the request by using an online tool : https://www.samltool.com/online_tools.php.

You can check how AuthN requests are used in SAML protocol in the following diagram :

This diagram shows the use case "SP-Initiated SSO". Refer to the technical overview mentioned above to have all details.

To generate the AuthnRequest we will use OpenSAML 3. As the website is stating there isn't a lot of documentation on this version of OpenSAML so I took some time to adapt existing code to get the snippet bellow. The original code can be found on this blog :  http://www.john-james-andersen.com/blog/programming/sample-saml-2-0-authnrequest-in-java.html (thanks to the author of this blog)


To make it run, add the following dependencies in your Maven project

<dependency>
    <groupId>org.opensaml</groupId>
    <artifactId>opensaml-core</artifactId>
    <version>3.3.0</version>
</dependency>
<dependency>
    <groupId>org.opensaml</groupId>
    <artifactId>opensaml-saml-api</artifactId>
    <version>3.3.0</version>
</dependency>
<dependency>
    <groupId>org.opensaml</groupId>
    <artifactId>opensaml-saml-impl</artifactId>
    <version>3.3.0</version>
</dependency>
<dependency>
    <groupId>net.shibboleth.utilities</groupId>
    <artifactId>java-support</artifactId>
    <version>7.3.0</version>
</dependency>

The last dependency (net.shibboleth.utilities) is for the pretty print of the SAML message.

By running the code, here there is the SAML AuthnRequest that is generated :

<?xml version="1.0" encoding="UTF-8"?>
<saml2p:AuthnRequest
    AssertionConsumerServiceURL="http://sp.example.com/demo1/index.php?acs"
    Destination="http://idp.example.com/SSOService.php"
    ForceAuthn="true" ID="ONELOGIN_6f319749-6db0-4ac6-be72-cb223d5870a4"
    IsPassive="false" IssueInstant="2017-10-01T18:20:31.096Z"
    ProtocolBinding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Artifact"
    Version="2.0" xmlns:saml2p="urn:oasis:names:tc:SAML:2.0:protocol">
    <saml2:Issuer xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">http://sp.example.com/demo1/metadata.php</saml2:Issuer>
    <saml2p:NameIDPolicy AllowCreate="true"
        Format="urn:oasis:names:tc:SAML:2.0:nameid-format:transient" SPNameQualifier="SERVICE_PROVIDER_ID"/>
    <saml2p:RequestedAuthnContext Comparison="minimum">
        <saml2:AuthnContextClassRef xmlns:saml2="urn:oasis:names:tc:SAML:2.0:assertion">urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml2:AuthnContextClassRef>
    </saml2p:RequestedAuthnContext>
</saml2p:AuthnRequest>

The last thing to do is to validate this message, we will use this nice online tool : https://www.samltool.com/validate_authn_req.php. Another way to validate the message would by using OpenSAML itself. It may be the subject of another post on this blog.

I hope this article will help you getting started with SAML message generation. To continue on the subject I will try to add digital signature to this generated message in order to improve security but it will be in another post.

Thank you for reading!