improve config docs for OIDCPreservePost; see #1320; thanks @primo44

Signed-off-by: Hans Zandbelt <[email protected]>

Author: zandbelt

auth_openidc.conf

@@ -1012,9 +1012,11 @@
 
 # Indicates whether POST data will be preserved across authentication requests (and discovery in case of multiple OPs).
 # This is designed to prevent data loss when a session timeout occurs in a (long) user filled HTML form.
-# It cannot handle arbitrary payloads for security (DOS) reasons, merely form-encoded user data.
-# Preservation is done via HTML 5 session storage: note that this can lead to private data exposure on shared terminals.
-# The default is "Off" (for security reasons). Can be configured on a per Directory/Location basis.
+# It cannot handle arbitrary payloads for security (DOS) reasons, merely form-encoded user data where the Content-Type
+# header value is application/x-www-form-urlencoded. See also:
+#  https://github.com/OpenIDC/mod_auth_openidc/wiki/Known-Limitations#post-data-preservation-1
+# Preservation is done via HTML 5 session storage in the browser: note that this can lead to private data exposure on shared terminals.
+# The default is "Off" (for security reasons). It can be configured on a per Directory/Location basis.
 #OIDCPreservePost [On|Off]
 
 # POST preserve and restore templates to be used with OIDCPreservePost