SSO Custom Auth Backend Support

[FragmentedPacket]

Environment

• Python version: 3.6
• Nautobot version: 1.0.3

Proposed Functionality

Currently, only social_core.backends are supported within Nautobot to properly redirect to an external login source due to the following code.

nautobot/nautobot/core/settings_funcs.py

Lines 28 to 33 in dd731f3

	@lru_cache(maxsize=5)
	def _sso_auth_enabled(auth_backends):
	for backend in auth_backends:
	if backend.startswith("social_core.backends"):
	return True
	return False

nautobot/nautobot/core/templates/inc/nav_menu.html

Lines 823 to 827 in dd731f3

	{% if SSO_AUTH_ENABLED %}
	<li><a href="{% url 'social:begin' backends.backends.0 %}?next={{ request.get_full_path | urlencode }}&{{ SAML_IDP }}"><i class="mdi mdi-login"></i> Log in</a></li>
	{% else %}
	<li><a href="{% url settings.LOGIN_URL %}?next={{ request.get_full_path | urlencode }}"><i class="mdi mdi-login"></i> Log in</a></li>
	{% endif %}

If would be great if this can potentially be overridden within nautobot_config.py via a setting of some sort or just be more relaxed in general. A few potential ideas.

from django.conf import settings

@lru_cache(maxsize=5)
def _sso_auth_enabled(auth_backends):
    for backend in auth_backends:
        if backend.startswith(settings["SOCIAL_AUTH_BACKEND_PREFIX"]):
            return True
    return False

or

@lru_cache(maxsize=5)
def _sso_auth_enabled(auth_backends):
    if len(auth_backends) > 1:
        return True
    return False

This is due to only one AUTHENTICATION_BACKEND being defined by default, but not sure it's safe to assume that if it's greater than one, the login redirect should be enabled.

I'm sure there are other ways as well. I'd be willing to implement this once a decision has been made.

Use Case

We're building a custom authentication backend (that may eventually get ported into Social Auth Core, but at this point that is too much overhead and I assume that others may need to develop their own custom auth backends that can't be open sourced.

Database Changes

N/A

External Dependencies

N/A

[jathanism]

Seems like a hybrid of your suggestion and an explicit ENABLE_SSO = True setting might be the winning combination here. Thanks @FragmentedPacket!