adding optional configuration for ADFS SAML compatibility

[BaconAndEggs]

@fangli , would you consider merging this pull request?

This is related to the issue #7

I bumped into a few issues getting a compatible integration with ADFS, and added a couple configuration options to allow accommodating ADFS's SAML2 interpretation.

The changes are to add optional settings to pass down to pysaml2 for allowing the addition of the pysaml2 entityid for authentication requests to populate the Issuer element, and a change to allow setting (or for ADFS, excluding) the Format property on the NameIDPolicy element via the pysaml2 name_id_format.

Also, a change in the setup.py to bump the version of pysaml2 to 4.5.0 to support the option to pass the name_id_format.

[srinathganesh1]

Hi, do you have sample values to be used when integrating with ADFS?

[BaconAndEggs]

@srinathganesh1 , yeah, here you go:

    SAML2_AUTH = {
        'METADATA_AUTO_CONF_URL': SAML_METADATA_URL,
        # 'DEFAULT_NEXT_URL': '/', # uncomment if we want to force landing page after auth
        'ATTRIBUTES_MAP': {  # Change Email/UserName/FirstName/LastName to corresponding SAML2 userprofile attributes.
            'email': 'http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress',
            'username': 'http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress',
            'first_name': 'http://schemas.xmlsoap.org/ws/2005/05/identity/claims/givenname',
            'last_name': 'http://schemas.xmlsoap.org/ws/2005/05/identity/claims/surname',
        },
        'ENTITY_ID': os.environ['SAML_ENTITY_ID'],
        'NAME_ID_FORMAT': 'None',
    }

With:
SAML_ENTITY_ID being something like https://my.apps.fqdn.com/saml2_auth/acs/
SAML_METADATA_URL being something like https://my.orgs.adfs.fqdn.com/FederationMetadata/2007-06/FederationMetadata.xml

Also, on the ADFS side, I had to ask the administrator to make a translation mapping to populate the NameID sub-element of the Subject element, which gets posted to the SP assertion endpoint. The instructions that we followed in doing this were from this Ping knowledge base article: https://ping.force.com/Support/PingIdentityArticle?id=kA3400000008TIRCA2 (you might need to make an account to read the article).

I hope that helps.

[srinathganesh1]

Thank you. will try that out