Check if the Authorization header for Basic Authentication is valid

If the header is not valid, DRF returns None when calling the
authenticate() method. This can cause troubles when users are
leveraging the remote authentication because Pulp thinks they
are using anonymous tokens. In the end, authorized users cannot
push or pull content from Pulp.

closes pulp#1577

CHANGES/1577.bugfix

@@ -0,0 +1 @@
+Fixed a bug that disallowed users from leveraging the remote authentication.

pulp_container/app/token_verification.py

@@ -64,8 +64,9 @@ class RegistryAuthentication(BasicAuthentication):
     A basic authentication class that accepts empty username and password as anonymous.
     """
 
-    PULP_AUTHENTICATION_CLASS = "pulpcore.app.authentication.PulpRemoteUserAuthentication"
+    PULP_REMOTE_AUTHENTICATION_CLASS = "pulpcore.app.authentication.PulpRemoteUserAuthentication"
     AUTH_CLASSES = settings.REST_FRAMEWORK["DEFAULT_AUTHENTICATION_CLASSES"]
+    ALLOWS_REMOTE_AUTHENTICATION = PULP_REMOTE_AUTHENTICATION_CLASS in AUTH_CLASSES
 
     def authenticate(self, request):
         """
@@ -80,13 +81,18 @@ def authenticate(self, request):
             return (AnonymousUser, None)
 
         try:
-            return super().authenticate(request)
+            result = super().authenticate(request)
         except AuthenticationFailed:
-            if self.PULP_AUTHENTICATION_CLASS in self.AUTH_CLASSES:
+            if self.ALLOWS_REMOTE_AUTHENTICATION:
                 return RemoteUserRegistryAuthentication().authenticate(request)
             else:
                 raise
 
+        if result is None and self.ALLOWS_REMOTE_AUTHENTICATION:
+            return RemoteUserRegistryAuthentication().authenticate(request)
+        else:
+            return result
+
 
 class RemoteUserRegistryAuthentication(RemoteUserAuthentication):
     """