Add SLO support

[deepakprabhakara]

From dnoliver:

Found a bug? Please fill out the sections below. 👍

Issue Summary

A summary of the issue. This needs to be a clear detailed-rich summary.

Not sure if this is a bug!
I am trying to use https://mocksaml.com as a mock for my idp for single sign on and single log out.
I am using the metadata url to configure my saml library https://github.com/SAML-Toolkits/python3-saml
So because the https://mocksaml.com metadata file doesn't have an SLO item, my lib tells me that SLO is not supported by the idp (which make sense).
But I also found some PRs and issues resolved related to slo (boxyhq/jackson#128, and boxyhq/saml20#14), so wanted to check if this is something that should be supported but its just missed from the public metadata file.

Steps to Reproduce

Well, for me, this is how I implemented SLO with the library I referenced.
The last line of the snippet throws: onelogin.saml2.errors.OneLogin_Saml2_Error: The IdP does not support Single Log Out

    from onelogin.saml2.auth import OneLogin_Saml2_Auth
    from onelogin.saml2.idp_metadata_parser import OneLogin_Saml2_IdPMetadataParser

    def logout(self, request):
        """Initialize SAML logout"""
        req = self.__prepare_tornado_request(request)
        idp_data = OneLogin_Saml2_IdPMetadataParser.parse_remote(
            self.saml_idp_metadata, timeout=5
        )
        self.saml_settings["idp"] = idp_data["idp"]
        auth = OneLogin_Saml2_Auth(req, self.saml_settings)
        return auth.logout(name_id=None, session_index=None)

But also, a simple way to show this problem is just to go to https://mocksaml.com/api/saml/metadata, and check for the following missing properties:

<SingleLogoutService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="<URL>"/>
<SingleLogoutService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-Redirect" Location="<URL>"/>

Any other relevant information. For example, why do you consider this a bug and what did you expect to happen instead?

I consider this a bug because I couldn't find docs saying if mocksaml supports slo or not, but I could find prs and issues referencing the support for slo. Maybe a "this service doesn't support slo" would be nice if that is the expectation

Technical details

• Browser version: You can use https://www.whatsmybrowser.org/ to find this out.: Chrome 120
• Node.js version: N/A (not using this as a lib, I'm using the service)
• Anything else that you think could be an issue.

Thanks for doing this! It has been super helpful to develop and test SAML integration so far!

[Stunext]

Any update on this?