apache: Increase OpenID Connect RP session timeout activity

Tests:

- Without patch, open FeatherWiki wiki and save after 5 minutes. Save fails.

- Apply the patch, Apache app setup is run and mod_auth_openidc configuration
is updated. Open FeatherWiki wiki and save after 5 minutes. Save works, wiki
contents are saved.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: Joseph Nuthalapati <njoseph@riseup.net>

plinth/modules/apache/__init__.py

@@ -86,7 +86,7 @@ class ApacheApp(app_module.App):
 
     app_id = 'apache'
 
-    _version = 16
+    _version = 17
 
     def __init__(self) -> None:
         """Create components for the app."""

plinth/modules/apache/privileged.py

@@ -237,6 +237,30 @@ def _setup_oidc_config():
 
     Keep the metadata directory and configuration file unreadable by non-admin
     users since they contain module's crypto secret and OIDC client secret.
+
+    # Session management
+
+    When apps like Syncthing are protected with mod_auth_openidc, there a
+    session maintained using server-side session storage and a cookie on the
+    client side. This session is different from the session managed by the
+    OpenID Connect Provider (FreedomBox web interface). As long as this session
+    is valid, no further authentication mechanisms are triggered.
+
+    When the session expires, if the request is a GET request (due to page
+    reload), the browser is redirected to OP, a fresh token is created, and the
+    page is loaded. However, for POST requests, 401 error is returned and if
+    the application is unaware, it won't do much about it. So, this
+    necessitates keeping the session timeout value high.
+
+    When logout is performed on FreedomBox web interface, mod_auth_openidc
+    cookie is also removed and logout feels instantaneous. However, this won't
+    work for applications not using mod_auth_openidc and for applications
+    hosted on other domains. A better way to do this is to implement OpenID
+    Connect's Back-Channel Logout or using OpenID Connect Session Management.
+
+    For more about session management see:
+    https://github.com/OpenIDC/mod_auth_openidc/wiki/Sessions-and-Timeouts and
+    https://github.com/OpenIDC/mod_auth_openidc/wiki/Session-Management-Settings
     """
     metadata_dir_path.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
     metadata_dir_path.mkdir(mode=0o700, exist_ok=True)
@@ -259,6 +283,13 @@ def _setup_oidc_config():
     OIDCSSLValidateServer Off
     OIDCProviderMetadataRefreshInterval 86400
 
+    # Expire the mod_auth_openidc session (not the OpenID Conneect Provider
+    # session) after 10 hours of idle with a maximum session duration equal to
+    # the expiry time of the ID token (10 hours). This allows applications such
+    # as FeatherWiki to have long editing sessions before save.
+    OIDCSessionInactivityTimeout 36000
+    OIDCSessionMaxDuration 0
+
     # Use relative URL to return to the original domain
     OIDCRedirectURI /apache/oidc/callback
     OIDCRemoteUserClaim sub