diff --git a/lib/ngx-oauth/config.lua b/lib/ngx-oauth/config.lua
index 33d19d6..63698f8 100644
--- a/lib/ngx-oauth/config.lua
+++ b/lib/ngx-oauth/config.lua
@@ -10,6 +10,7 @@ local map             = util.map
 local par             = util.partial
 local starts_with     = util.starts_with
 
+local oauth_config_prefix = nil
 local DEFAULTS = {
   client_id         = '',
   client_secret     = '',
@@ -30,7 +31,7 @@ local OAAS_ENDPOINT_VARS = {'authorization_url', 'token_url', 'userinfo_url'}
 
 
 local load_from_ngx = par(map, function(default_value, key)
-    return util.default(ngx.var['oauth_'..key], default_value)
+    return util.default(ngx.var[oauth_config_prefix..key], default_value)
   end, DEFAULTS)
 
 local function validate (conf)
@@ -71,6 +72,7 @@ local M = {}
 -- @treturn nil|string Validation error, or `false` if no validation
 --   error was found.
 function M.load ()
+  oauth_config_prefix = ngx.var['oauth_config_prefix'] or 'oauth_'
   local conf = load_from_ngx()
 
   if not is_absolute_url(conf.redirect_uri) then