davt

davt is a lua module for nginx to aid with impersonation. Its target use case is for use with WebDAV, so that all operations are executed as the user in the request.

For every incoming request, davt enables nginx to switch the OS user (with setfsuid) and/or group IDs/supplementary group IDs (via setfsgid, setgroups, initgroups) to match the authenticated user or specific groups before performing any file opertions.

As davt enables impersonation, a few properties follow:

• The files do NOT need to be owned by an nginx service account user, nor does an ACL need to be modified to allow for access to an service group (for filesystems supporting ACLs). This allows you to transperently operate the service over existing directories.

• Ownership when creating files is preserved for the files in question. This ensures that files created for the user via WebDAV are also readable when the user is in a shell, for example.

Requirements

davt requires ljsyscall. It also used the ffi library from LuaJIT.

Deployment

davt is only compatible with Linux. davt must be ran as root. It is recommended that you drop all capabilities EXCEPT CAP_SETGID and CAP_SETUID, although it seems like CAP_SETPCAP may be necessary, as well as CAP_NET_BIND_SERVICE if you want to bind to a privileged port (ports 80, 443, etc...).

As davt allows impersonation, all incoming requests to davt MUST match a preset secret that the davt lua object is configured with. If it is desired to disable checkin, setting the secret explicitly to the empty string can be used, as in the following example:

local lua_davt = require("davt")
local davt = lua_davt:new({secret = ""})

If no secret is explicitly set, davt will set a random secret at startup, printing that secret out to the log. The following code will do that:

local lua_davt = require("davt")
local davt = lua_davt:new()