Optionally pass REMOTE_USER to application - apache

Question

In our company we have an apache server running a django application (through wsgi) and some legacy php applications. To have some sort of single sign on we decided to use mod_auth_form and wsgi as the AuthFormProvider.
In django itself we enabled the RemoteUserBackend and all works fine.
The legacy php applications are also protected via mod_auth_form and wsgi.
The problem is that there are some locations which should be accessible by authenticated and anonymous users where authenticated users have some sort of extras (like personal greeting or an enabled logout button).
With our current configuration however I can't figure out to tell apache to set REMOTE_USER if a user has logged in previously but does not ask for a password if the user is not logged in.
I will try to give an example of what I want to accomplish.
This is an example configuration.
<Location "/protected-zone">
AuthType basic
AuthName "private area"
AuthBasicProvider file
AuthUserFile /usr/local/etc/apache2/userfile.htaccess
<RequireAll>
Require valid-user
</RequireAll>
</Location>
<Location "/mixed-zone">
AuthType basic
AuthName "private area"
AuthBasicProvider file
AuthUserFile /usr/local/etc/apache2/userfile.htaccess
<RequireAll>
Require [todo]
</RequireAll>
</Location>
If users go to /protected-zone they should be asked for a password - that's quite easy.
If the user then goes to /mixed-zone (after sucessfull login) he or she should be greeted with their username (based on the header REMOTE_USER).
If an unauthenticated user goes to /mixed-zone he or she should not be prompted to enter credentials.
What we've tried so far was to omit the ReqireAll tag in /mixed-zone which causes apache to never set REMOTE_USER even if the user was logged in before.

Answer 1

Thanks to the comment about sessions I was finally able to fix the problem in our specific case.
We now use sessions like in the example below.
SessionMaxAge [age in seconds]
SessionCookieName session-cookie path=/;httponly;secure;version=1
SessionCryptoPassphrase [some random string]
<Location "/protected-zone">
Session On
SessionEnv On
AuthType basic
AuthName "private"
AuthBasicProvider file
AuthUserFile /usr/local/etc/apache2/userfile.htaccess
<RequireAll>
Require valid-user
</RequireAll>
</Location>
<Location "/mixed-zone">
Session On
SessionEnv On
</Location>
With SessionEnv set to On apache sets an additional HTTP_SESSION header in the request which may be used by the underlying application (see PHP example below)
<?php
$session = array();
parse_str($_SERVER['HTTP_SESSION'], $session);
$username = $session['private-user'];
?>
Since we use django I wrote a small middleware which is executed before RemoteUserMiddleware and sets REMOTE_USER according to the user in the session if it was not specified previously.
from urllib.parse import parse_qs # works in pyhton3
class SessionUserMiddleware (object):
"""
Middleware to extract a user from a session if no REMOTE_USER is set.
"""
header = "REMOTE_USER"
session_header = "HTTP_SESSION"
session_key = "private-user"
def process_request(self, request):
if self.header not in request.META or not request.META[self.header]:
try:
username = parse_qs(request.META[self.session_header])[self.session_key]
request.META[self.header] = username
except KeyError:
pass