[fix] Allowed managing social auth secrets when needed

Before, OpenWISP Users removed the ``allauth.socialaccount``
admin sections to keep the admin UI simple, but over time
more users need this to support OAuth/SAML authentication
to the admin interface (manage app secrets).
With this change, the admin allows managing app secrets
if any ``allauth.socialaccount.provider`` is installed,
eg: microsoft, google, openid, etc.

[backport 1.2]

(cherry picked from commit 8c19f71)

Author: nemesifier

openwisp_users/admin.py

@@ -652,11 +652,14 @@ def get_user(self, obj):
     admin.site.unregister(EmailAddress)
 
 if allauth_settings.SOCIALACCOUNT_ENABLED:
-    for model in [
-        ("socialaccount", "SocialApp"),
+    socialaccount_models = [
         ("socialaccount", "SocialToken"),
         ("socialaccount", "SocialAccount"),
-    ]:
+    ]
+    # Allow managing secrets if OAuth/SAML is enabled
+    if not app_settings.SOCIALACCOUNT_ADMIN_NEEDED:
+        socialaccount_models.append(("socialaccount", "SocialApp"))
+    for model in socialaccount_models:
         model_class = apps.get_model(*model)
         if admin.site.is_registered(model_class):
             admin.site.unregister(model_class)

openwisp_users/settings.py

@@ -49,3 +49,12 @@
         "openwisp_users.views.AutocompleteJsonView",
     ),
 )
+
+# if OAuth/SAML is enabled, allow manging keys/secrets
+if any(
+    app.startswith("allauth.socialaccount.providers") for app in settings.INSTALLED_APPS
+):  # pragma: no cover
+    SOCIALACCOUNT_ADMIN_NEEDED = True
+# otherwise hide the socialaccount admin (not needed)
+else:
+    SOCIALACCOUNT_ADMIN_NEEDED = False