commit 912aa852ebd78577f59cf7958c709acea98ace4c
Author: John Dennis <jdennis@redhat.com>
Date:   Fri Apr 8 09:01:22 2016 -0400

    am_check_uid() should be no-op if mellon not enabled
    
    mod_auth_mellon was interferring with other Apache authentication
    modules (e.g. mod_auth_kerb) because when the Apache check_user_id
    hook ran the logic in am_check_uid would execute even if mellon was
    not enabled for the location. This short circuited the hook execution
    and never allowed the authentication enabled for the location to
    execute. It resulted in HTTP_UNAUTHORIZED being returned with the
    client then expecting a WWW-Authenticate header field causing the
    client to attempt to authenticate again.
    
    Signed-off-by: John Dennis <jdennis@redhat.com>

diff --git a/auth_mellon_handler.c b/auth_mellon_handler.c
index a72e1ca..864396f 100644
--- a/auth_mellon_handler.c
+++ b/auth_mellon_handler.c
@@ -3625,6 +3625,12 @@ int am_check_uid(request_rec *r)
         return OK;
     }
 
+    /* Check that the user has enabled authentication for this directory. */
+    if(dir->enable_mellon == am_enable_off
+       || dir->enable_mellon == am_enable_default) {
+	return DECLINED;
+    }
+
 #ifdef HAVE_ECP
     am_req_cfg_rec *req_cfg = am_get_req_cfg(r);
     if (req_cfg->ecp_authn_req) {