Updates _sp_authn_requests_signed_alg to work with multiple bindings

[mobleyc]

_sp_authn_requests_signed_alg allows overriding the algorithm used with SignatureMethod but currently only works with the BINDING_HTTP_REDIRECT. This change enables its use for both BINDING_HTTP_REDIRECT and BINDING_HTTP_POST, during login and its use during logout.

The motivation for this change is ADFS defaults to requiring SHA256.

This change was tested with Apache Shibboleth and ADFS on Windows Server 2012.

[peppelinux]

I think that would be better enable this feature in pySAML2, made a related PR here:
IdentityPython/pysaml2#597

[peppelinux]

Hi @mobleyc, have you seen the pySAML2 PR I referenced, would you like to spend some words on?
I'm going to manage the old PR and a feedback from you will be really appreciated

[peppelinux]

Hi @mobleyc
here we have a default behaviour:
https://github.com/knaperek/djangosaml2/blob/8d9b692b10dae2613574baf5857513b35e5f0ce1/djangosaml2/views.py#L174

As far I tested the signed authentication requests in pySAML2 works in HTTP_POST binding and there we have this check.

Is there some tests that you would like to share here?
I disabled HTTP_REDIRECT in my implementations because of this

[mobleyc]

Hi the issue I encountered is not signing, it's the ability to configure the signing algorithm. Currently this line. ADFS uses sha256 by default and there is not way to override this using the BINDING_HTTP_POST binding.

I can add a comment to the pySAML ticket in support of the PR if that helps.

And thank you for your help with this!

[peppelinux]

Thank you @mobleyc,

I have fixed this features, because I use SHA256 in djangosaml2 in a federation that want it, with that PR you find in pySAML2.

Regarding the general refactor you've done I think that's quite good. So if you are ready for that I would ask you to have a test with the current master branch of djangosaml2, because with the current implementation if a signing is required it alway rely on HTTP_POST, see:
https://github.com/knaperek/djangosaml2/blob/312a06529198ebf4a9e12263b9f0a10725fbb6bd/djangosaml2/views.py#L175

Do a test then we decide what to do, I would accept your PR with pleasure,
thanks for feedback

[peppelinux]

I think that also this should be considered

#193

[peppelinux]

Hi, please can you fix the conflicting files?
I think it's time to merge it

[peppelinux]

Due to missing reply but thank you for your idea